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class="mw-body-content"><script>function mfTempOpenSection(id){var block=document.getElementById("mf-section-"+id);block.className+=" open-block";block.previousSibling.className+=" open-block";}</script><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><section class="mf-section-0" id="mf-section-0"> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"Free radical" redirects here. For the aging theory, see <a href="/wiki/Free-radical_theory_of_aging" title="Free-radical theory of aging">Free-radical theory of aging</a>. For other uses, see <a href="/wiki/Free_radical_(disambiguation)" class="mw-disambig" title="Free radical (disambiguation)">Free radical (disambiguation)</a>.</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">This article is about free radicals. For radicals within larger molecules, see <a href="/wiki/Moiety_(chemistry)" title="Moiety (chemistry)">Moiety (chemistry)</a>.</div> <p>In <a href="/wiki/Chemistry" title="Chemistry">chemistry</a>, a <b>radical</b>, also known as a <b>free radical</b>, is an <a href="/wiki/Atom" title="Atom">atom</a>, <a href="/wiki/Molecule" title="Molecule">molecule</a>, or <a href="/wiki/Ion" title="Ion">ion</a> that has at least one <a href="/wiki/Unpaired_electron" title="Unpaired electron">unpaired valence electron</a>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> With some exceptions, these unpaired electrons make radicals highly <a href="/wiki/Chemical_reaction" title="Chemical reaction">chemically reactive</a>. Many radicals spontaneously <a href="/wiki/Dimer_(chemistry)" class="mw-redirect" title="Dimer (chemistry)">dimerize</a>. Most organic radicals have short lifetimes. </p><figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Hydroxyl_radical.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/Hydroxyl_radical.svg/110px-Hydroxyl_radical.svg.png" decoding="async" width="110" height="76" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/db/Hydroxyl_radical.svg/165px-Hydroxyl_radical.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/db/Hydroxyl_radical.svg/220px-Hydroxyl_radical.svg.png 2x" data-file-width="42" data-file-height="29"></a><figcaption>The <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radical</a>, <a href="/wiki/Lewis_structure" title="Lewis structure">Lewis structure</a> shown, contains one unpaired electron.</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Hydroxide_vs_hydroxyl.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Hydroxide_vs_hydroxyl.svg/220px-Hydroxide_vs_hydroxyl.svg.png" decoding="async" width="220" height="100" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Hydroxide_vs_hydroxyl.svg/330px-Hydroxide_vs_hydroxyl.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8b/Hydroxide_vs_hydroxyl.svg/440px-Hydroxide_vs_hydroxyl.svg.png 2x" data-file-width="152" data-file-height="69"></a><figcaption> <a href="/wiki/Lewis_dot_structure" class="mw-redirect" title="Lewis dot structure">Lewis dot structure</a> of a <a href="/wiki/Hydroxide" title="Hydroxide">Hydroxide</a> ion compared to a <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radical</a></figcaption></figure> <p>A notable example of a radical is the <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radical</a> (HO<b>·</b>), a molecule that has one unpaired electron on the oxygen atom. Two other examples are <a href="/wiki/Triplet_oxygen" title="Triplet oxygen">triplet oxygen</a> and <a href="/wiki/Methylene_radical" class="mw-redirect" title="Methylene radical">triplet carbene</a> (<b>꞉</b><span class="chemf nowrap">CH<span class="nowrap"><span style="display:inline-block;margin-bottom:-0.3em;vertical-align:-0.4em;line-height:1em;font-size:80%;text-align:left"><sup style="font-size:inherit;line-height:inherit;vertical-align:baseline"></sup><br><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">2</sub></span></span></span>) which have two unpaired electrons. </p><p>Radicals may be generated in a number of ways, but typical methods involve <a href="/wiki/Redox_reaction" class="mw-redirect" title="Redox reaction">redox reactions</a>, <a href="/wiki/Ionizing_radiation" title="Ionizing radiation">ionizing radiation</a>, heat, electrical discharges, and <a href="/wiki/Electrolysis" title="Electrolysis">electrolysis</a> are known to produce radicals. Radicals are intermediates in many chemical reactions, more so than is apparent from the balanced equations. </p><p>Radicals are important in <a href="/wiki/Combustion" title="Combustion">combustion</a>, <a href="/wiki/Atmospheric_chemistry" title="Atmospheric chemistry">atmospheric chemistry</a>, <a href="/wiki/Polymerization" title="Polymerization">polymerization</a>, <a href="/wiki/Plasma_(physics)" title="Plasma (physics)">plasma</a> chemistry, <a href="/wiki/Biochemistry" title="Biochemistry">biochemistry</a>, and many other chemical processes. A majority of natural products are generated by radical-generating enzymes. In living organisms, the radicals <a href="/wiki/Superoxide" title="Superoxide">superoxide</a> and <a href="/wiki/Nitric_oxide" title="Nitric oxide">nitric oxide</a> and their reaction products regulate many processes, such as control of vascular tone and thus blood pressure. They also play a key role in the intermediary metabolism of various biological compounds. Such radicals can even be messengers in a process dubbed <a href="/wiki/Redox_signaling" class="mw-redirect" title="Redox signaling">redox signaling</a>. A radical may be trapped within a <a href="/wiki/Cage_effect_(chemistry)" class="mw-redirect" title="Cage effect (chemistry)">solvent cage</a> or be otherwise bound. </p> <div id="toc" class="toc" role="navigation" aria-labelledby="mw-toc-heading"><input type="checkbox" role="button" id="toctogglecheckbox" class="toctogglecheckbox" style="display:none"><div class="toctitle" lang="en" dir="ltr"><h2 id="mw-toc-heading">Contents</h2><span class="toctogglespan"><label class="toctogglelabel" for="toctogglecheckbox"></label></span></div> <ul> <li class="toclevel-1 tocsection-1"><a href="#Formation"><span class="tocnumber">1</span> <span class="toctext">Formation</span></a> <ul> <li class="toclevel-2 tocsection-2"><a href="#Radical_formation_from_spin-paired_molecules"><span class="tocnumber">1.1</span> <span class="toctext">Radical formation from spin-paired molecules</span></a> <ul> <li class="toclevel-3 tocsection-3"><a href="#Homolysis"><span class="tocnumber">1.1.1</span> <span class="toctext">Homolysis</span></a></li> <li class="toclevel-3 tocsection-4"><a href="#Reduction"><span class="tocnumber">1.1.2</span> <span class="toctext">Reduction</span></a></li> </ul> </li> <li class="toclevel-2 tocsection-5"><a href="#Radical_formation_from_other_radicals"><span class="tocnumber">1.2</span> <span class="toctext">Radical formation from other radicals</span></a> <ul> <li class="toclevel-3 tocsection-6"><a href="#Abstraction"><span class="tocnumber">1.2.1</span> <span class="toctext">Abstraction</span></a></li> <li class="toclevel-3 tocsection-7"><a href="#Addition"><span class="tocnumber">1.2.2</span> <span class="toctext">Addition</span></a></li> <li class="toclevel-3 tocsection-8"><a href="#Elimination"><span class="tocnumber">1.2.3</span> <span class="toctext">Elimination</span></a></li> </ul> </li> </ul> </li> <li class="toclevel-1 tocsection-9"><a href="#Stability"><span class="tocnumber">2</span> <span class="toctext">Stability</span></a> <ul> <li class="toclevel-2 tocsection-10"><a href="#Stability_of_organic_radicals"><span class="tocnumber">2.1</span> <span class="toctext">Stability of organic radicals</span></a> <ul> <li class="toclevel-3 tocsection-11"><a href="#Electronegativity"><span class="tocnumber">2.1.1</span> <span class="toctext">Electronegativity</span></a></li> <li class="toclevel-3 tocsection-12"><a href="#Delocalization"><span class="tocnumber">2.1.2</span> <span class="toctext">Delocalization</span></a></li> <li class="toclevel-3 tocsection-13"><a href="#Steric_hindrance"><span class="tocnumber">2.1.3</span> <span class="toctext">Steric hindrance</span></a></li> <li class="toclevel-3 tocsection-14"><a href="#Facile_H-atom_donors"><span class="tocnumber">2.1.4</span> <span class="toctext">Facile H-atom donors</span></a></li> </ul> </li> </ul> </li> <li class="toclevel-1 tocsection-15"><a href="#Inorganic_radicals"><span class="tocnumber">3</span> <span class="toctext">Inorganic radicals</span></a></li> <li class="toclevel-1 tocsection-16"><a href="#Diradicals"><span class="tocnumber">4</span> <span class="toctext">Diradicals</span></a></li> <li class="toclevel-1 tocsection-17"><a href="#Occurrence_of_radicals"><span class="tocnumber">5</span> <span class="toctext">Occurrence of radicals</span></a> <ul> <li class="toclevel-2 tocsection-18"><a href="#Combustion"><span class="tocnumber">5.1</span> <span class="toctext">Combustion</span></a></li> <li class="toclevel-2 tocsection-19"><a href="#Polymerization"><span class="tocnumber">5.2</span> <span class="toctext">Polymerization</span></a></li> <li class="toclevel-2 tocsection-20"><a href="#Atmospheric_radicals"><span class="tocnumber">5.3</span> <span class="toctext">Atmospheric radicals</span></a></li> <li class="toclevel-2 tocsection-21"><a href="#In_biology"><span class="tocnumber">5.4</span> <span class="toctext">In biology</span></a></li> <li class="toclevel-2 tocsection-22"><a href="#Reactive_oxygen_species"><span class="tocnumber">5.5</span> <span class="toctext">Reactive oxygen species</span></a></li> </ul> </li> <li class="toclevel-1 tocsection-23"><a href="#Depiction_in_chemical_reactions"><span class="tocnumber">6</span> <span class="toctext">Depiction in chemical reactions</span></a></li> <li class="toclevel-1 tocsection-24"><a href="#History_and_nomenclature"><span class="tocnumber">7</span> <span class="toctext">History and nomenclature</span></a></li> <li class="toclevel-1 tocsection-25"><a href="#See_also"><span class="tocnumber">8</span> <span class="toctext">See also</span></a></li> <li class="toclevel-1 tocsection-26"><a href="#References"><span class="tocnumber">9</span> <span class="toctext">References</span></a></li> </ul> </div> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(1)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Formation">Formation</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=1" title="Edit section: Formation" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-1 collapsible-block" id="mf-section-1"> <p>Radicals are either (1) formed from spin-paired molecules or (2) from other radicals. Radicals are formed from spin-paired molecules through <a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">homolysis</a> of weak bonds or electron transfer, also known as reduction. Radicals are formed from other radicals through substitution, <a href="/wiki/Addition" title="Addition">addition</a>, and elimination reactions. </p> <div class="mw-heading mw-heading3"><h3 id="Radical_formation_from_spin-paired_molecules">Radical formation from spin-paired molecules</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=2" title="Edit section: Radical formation from spin-paired molecules" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <div class="mw-heading mw-heading4"><h4 id="Homolysis">Homolysis</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=3" title="Edit section: Homolysis" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Bromine_homolysis.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Bromine_homolysis.svg/220px-Bromine_homolysis.svg.png" decoding="async" width="220" height="46" class="mw-file-element" data-file-width="154" data-file-height="32"></noscript><span class="lazy-image-placeholder" style="width: 220px;height: 46px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Bromine_homolysis.svg/220px-Bromine_homolysis.svg.png" data-width="220" data-height="46" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Bromine_homolysis.svg/330px-Bromine_homolysis.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Bromine_homolysis.svg/440px-Bromine_homolysis.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Homolysis of a bromine molecule producing two bromine radicals</figcaption></figure> <p><a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">Homolysis</a> makes two new radicals from a spin-paired molecule by breaking a covalent bond, leaving each of the fragments with one of the electrons in the bond.<sup id="cite_ref-:1_3-0" class="reference"><a href="#cite_note-:1-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Because breaking a chemical bond requires energy, <a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">homolysis</a> occurs under the addition of heat or light. The <a href="/wiki/Bond-dissociation_energy" title="Bond-dissociation energy">bond dissociation energy</a> associated with homolysis depends on the stability of a given compound, and some weak bonds are able to homolyze at relatively lower temperatures. </p><p>Some homolysis reactions are particularly important because they serve as an initiator for other radical reactions. One such example is the homolysis of halogens, which occurs under light and serves as the driving force for radical halogenation reactions. </p><p>Another notable reaction is the homolysis of dibenzoyl peroxide, which results in the formation of two benzoyloxy radicals and acts as an initiator for many radical reactions.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Homolysis2.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Homolysis2.svg/430px-Homolysis2.svg.png" decoding="async" width="430" height="78" class="mw-file-element" data-file-width="406" data-file-height="74"></noscript><span class="lazy-image-placeholder" style="width: 430px;height: 78px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Homolysis2.svg/430px-Homolysis2.svg.png" data-width="430" data-height="78" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Homolysis2.svg/645px-Homolysis2.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Homolysis2.svg/860px-Homolysis2.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Homolysis of dibenzoyl peroxide producing two benzoyloxy radicals</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Reduction">Reduction</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=4" title="Edit section: Reduction" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Lithium_Naphthalenide.jpg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Lithium_Naphthalenide.jpg/120px-Lithium_Naphthalenide.jpg" decoding="async" width="120" height="222" class="mw-file-element" data-file-width="2477" data-file-height="4581"></noscript><span class="lazy-image-placeholder" style="width: 120px;height: 222px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Lithium_Naphthalenide.jpg/120px-Lithium_Naphthalenide.jpg" data-width="120" data-height="222" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Lithium_Naphthalenide.jpg/180px-Lithium_Naphthalenide.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Lithium_Naphthalenide.jpg/240px-Lithium_Naphthalenide.jpg 2x" data-class="mw-file-element"> </span></a><figcaption>The deep colour of <a href="/wiki/Lithium_naphthalene" title="Lithium naphthalene">lithium naphthalene</a> results from the lithium naphthanide radical.</figcaption></figure> <p>Classically, radicals form by one-electron <a href="/wiki/Redox" title="Redox">reductions</a>. Typically one-electron reduced organic compounds are unstable. Stability is conferred to the radical anion when the charge can be <a href="/wiki/Delocalization" class="mw-redirect" title="Delocalization">delocalized</a>. Examples include alkali metal <a href="/wiki/Lithium_naphthalene" title="Lithium naphthalene">naphthenides</a>, <a href="/wiki/Anthracene" title="Anthracene">anthracenides</a>, and <a href="/wiki/Ketyl" title="Ketyl">ketyls</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Radical_formation_from_other_radicals">Radical formation from other radicals</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=5" title="Edit section: Radical formation from other radicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <div class="mw-heading mw-heading4"><h4 id="Abstraction">Abstraction</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=6" title="Edit section: Abstraction" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Abstraction.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Abstraction.svg/430px-Abstraction.svg.png" decoding="async" width="430" height="86" class="mw-file-element" data-file-width="352" data-file-height="70"></noscript><span class="lazy-image-placeholder" style="width: 430px;height: 86px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Abstraction.svg/430px-Abstraction.svg.png" data-width="430" data-height="86" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Abstraction.svg/645px-Abstraction.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f4/Abstraction.svg/860px-Abstraction.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Radical abstraction between a benzoyloxy radical and hydrogen bromide</figcaption></figure> <p><a href="/wiki/Hydrogen_atom_abstraction" title="Hydrogen atom abstraction">Hydrogen abstraction</a> generates radicals. To achieve this reaction, the C-H bond of the H-atom donor must be weak, which is rarely the case in organic compounds. <a href="/wiki/Allylic" class="mw-redirect" title="Allylic">Allylic</a> and especiall doubly allylic C-H bonds are prone to abstraction by O<sub>2</sub>. This reaction is the basis of <a href="/wiki/Drying_oil" title="Drying oil">drying oils</a>, such as <a href="/wiki/Linoleic_acid" title="Linoleic acid">linoleic acid</a> derivatives. </p> <div class="mw-heading mw-heading4"><h4 id="Addition">Addition</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=7" title="Edit section: Addition" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Radicaladdition.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Radicaladdition.svg/250px-Radicaladdition.svg.png" decoding="async" width="250" height="54" class="mw-file-element" data-file-width="217" data-file-height="47"></noscript><span class="lazy-image-placeholder" style="width: 250px;height: 54px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Radicaladdition.svg/250px-Radicaladdition.svg.png" data-width="250" data-height="54" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Radicaladdition.svg/375px-Radicaladdition.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/83/Radicaladdition.svg/500px-Radicaladdition.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Radical addition of a bromine radical to a substituted alkene</figcaption></figure> <p>In <a href="/wiki/Free-radical_addition" title="Free-radical addition">free-radical additions</a>, a radical adds to a spin-paired substrate. When applied to organic compounds, the reaction usually entails addition to an alkene. This addition generates a new radical, which can add to yet another alkene, etc. This behavior underpins <a href="/wiki/Radical_polymerization" title="Radical polymerization">radical polymerization</a>, technology that produces many <a href="/wiki/Plastic" title="Plastic">plastics</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Elimination">Elimination</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=8" title="Edit section: Elimination" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p>Radical elimination can be viewed as the reverse of radical addition. In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Radicalelimination.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Radicalelimination.svg/390px-Radicalelimination.svg.png" decoding="async" width="390" height="105" class="mw-file-element" data-file-width="261" data-file-height="70"></noscript><span class="lazy-image-placeholder" style="width: 390px;height: 105px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Radicalelimination.svg/390px-Radicalelimination.svg.png" data-width="390" data-height="105" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Radicalelimination.svg/585px-Radicalelimination.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Radicalelimination.svg/780px-Radicalelimination.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>A radical elimination reaction of a benzoyloxy radical</figcaption></figure> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(2)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Stability">Stability</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=9" title="Edit section: Stability" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-2 collapsible-block" id="mf-section-2"> <div class="mw-heading mw-heading3"><h3 id="Stability_of_organic_radicals">Stability of organic radicals</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=10" title="Edit section: Stability of organic radicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Vitamin_E_radical.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Vitamin_E_radical.svg/330px-Vitamin_E_radical.svg.png" decoding="async" width="330" height="86" class="mw-file-element" data-file-width="1170" data-file-height="305"></noscript><span class="lazy-image-placeholder" style="width: 330px;height: 86px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Vitamin_E_radical.svg/330px-Vitamin_E_radical.svg.png" data-width="330" data-height="86" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Vitamin_E_radical.svg/495px-Vitamin_E_radical.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Vitamin_E_radical.svg/660px-Vitamin_E_radical.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>The radical derived from <i><a href="/wiki/Tocopherol" title="Tocopherol">α-tocopherol</a></i></figcaption></figure> <p>The generation and reactivity of organic radicals are dependent on both their thermodynamic stability and kinetic stability, also known as the persistency. This distinction is necessary because these two types of stability do not always correlate with each other. For example, benzylic radicals, which are known for their weak benzylic C−H bond strength, are thermodynamically stabilized due to resonance delocalization. However, these radicals are kinetically transient because they can undergo rapid, diffusion-limited dimerization, resulting in a lifetime that is less than a few nanoseconds. To avoid confusion, particularly for carbon-centered radicals, Griller and Ingold introduced the following definitions:<sup id="cite_ref-:2_8-0" class="reference"><a href="#cite_note-:2-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> "Stabilized should be used to describe a carbon-centered radical, R<b>·</b>, when the R−H bond strength is weaker than the appropriate C−H bond of alkane." "Persistent should be used to describe a radical that has a lifetime that is significantly greater than methyl [radical] under the same condition." While relationships between thermodynamic stability and kinetic persistency is highly case-dependent, organic radicals can be generally stabilized by any or all of these factors: the presence of electronegativity, delocalization, and steric hindrance.<sup id="cite_ref-:2_8-1" class="reference"><a href="#cite_note-:2-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> The compound <a href="/wiki/TEMPO" title="TEMPO">2,2,6,6-tetramethylpiperidinyloxyl</a> illustrates the combination of all three factors. It is a commercially available solid that, aside from being magnetic, behaves like a normal organic compound. </p> <div class="mw-heading mw-heading4"><h4 id="Electronegativity">Electronegativity</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=11" title="Edit section: Electronegativity" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p>Organic radicals are inherently electron deficient thus the greater the electronegativity of the atom on which the unpaired electron resides the less stable the radical.<sup id="cite_ref-:0_9-0" class="reference"><a href="#cite_note-:0-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> Between carbon, nitrogen, and oxygen, for example, carbon is the most stable and oxygen the least stable. </p><p>Electronegativity also factors into the stability of carbon atoms of different hybridizations. Greater s-character correlates to higher electronegativity of the carbon atom (due to the close proximity of s orbitals to the nucleus), and the greater the electronegativity the less stable a radical.<sup id="cite_ref-:0_9-1" class="reference"><a href="#cite_note-:0-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> sp-hybridized carbons (50% s-character) form the least stable radicals compared to sp<sup>3</sup>-hybridized carbons (25% s-character) which form the most stable radicals. </p> <div class="mw-heading mw-heading4"><h4 id="Delocalization">Delocalization</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=12" title="Edit section: Delocalization" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p>The delocalization of electrons across the structure of a radical, also known as its ability to form one or more resonance structures, allows for the electron deficiency to be spread over several atoms, minimizing instability. Delocalization usually occurs in the presence of electron-donating groups, such as hydroxyl groups (−OH), ethers (−OR), adjacent alkenes, and amines (−NH<sub>2</sub> or −NR), or electron-withdrawing groups, such as C=O or C≡N.<sup id="cite_ref-:1_3-1" class="reference"><a href="#cite_note-:1-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Electron-Donating_Diagram.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/af/Electron-Donating_Diagram.svg/290px-Electron-Donating_Diagram.svg.png" decoding="async" width="290" height="209" class="mw-file-element" data-file-width="521" data-file-height="375"></noscript><span class="lazy-image-placeholder" style="width: 290px;height: 209px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/a/af/Electron-Donating_Diagram.svg/290px-Electron-Donating_Diagram.svg.png" data-width="290" data-height="209" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/af/Electron-Donating_Diagram.svg/435px-Electron-Donating_Diagram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/af/Electron-Donating_Diagram.svg/580px-Electron-Donating_Diagram.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Molecular orbital diagram of a radical with an electron-donating group</figcaption></figure> <p>Delocalization effects can also be understood using <a href="/wiki/Molecular_orbital_theory" title="Molecular orbital theory">molecular orbital theory</a> as a lens, more specifically, by examining the intramolecular interaction of the unpaired electron with a donating group's pair of electrons or the empty π* orbital of an electron-withdrawing group in the form of a molecular orbital diagram. The HOMO of a radical is singly-occupied hence the orbital is aptly referred to as the SOMO, or the Singly-Occupied Molecular Orbital. For an electron-donating group, the SOMO interacts with the lower energy lone pair to form a new lower-energy filled bonding-orbital and a singly-filled new SOMO, higher in energy than the original. While the energy of the unpaired electron has increased, the decrease in energy of the lone pair forming the new bonding orbital outweighs the increase in energy of the new SOMO, resulting in a net decrease of the energy of the molecule. Therefore, electron-donating groups help stabilize radicals. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Electron-Withdrawing_Diagram.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Electron-Withdrawing_Diagram.svg/290px-Electron-Withdrawing_Diagram.svg.png" decoding="async" width="290" height="197" class="mw-file-element" data-file-width="551" data-file-height="375"></noscript><span class="lazy-image-placeholder" style="width: 290px;height: 197px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Electron-Withdrawing_Diagram.svg/290px-Electron-Withdrawing_Diagram.svg.png" data-width="290" data-height="197" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Electron-Withdrawing_Diagram.svg/435px-Electron-Withdrawing_Diagram.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Electron-Withdrawing_Diagram.svg/580px-Electron-Withdrawing_Diagram.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Molecular orbital diagram of a radical with an electron-withdrawing group</figcaption></figure> <p>With a group that is instead electron-withdrawing, the SOMO then interacts with the empty π* orbital. There are no electrons occupying the higher energy orbital formed, while a new SOMO forms that is lower in energy. This results in a lower energy and higher stability of the radical species. Both donating groups and withdrawing groups stabilize radicals. </p><p>Another well-known albeit weaker form of delocalization is <a href="/wiki/Hyperconjugation" title="Hyperconjugation">hyperconjugation</a>. In radical chemistry, radicals are stabilized by hyperconjugation with adjacent alkyl groups. The donation of sigma (σ) C−H bonds into the partially empty radical orbitals helps to differentiate the stabilities of radicals on tertiary, secondary, and primary carbons. Tertiary carbon radicals have three σ C-H bonds that donate, secondary radicals only two, and primary radicals only one. Therefore, tertiary radicals are the most stable and primary radicals the least stable. </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Radical_hyperconjugation.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Radical_hyperconjugation.svg/350px-Radical_hyperconjugation.svg.png" decoding="async" width="350" height="86" class="mw-file-element" data-file-width="487" data-file-height="119"></noscript><span class="lazy-image-placeholder" style="width: 350px;height: 86px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Radical_hyperconjugation.svg/350px-Radical_hyperconjugation.svg.png" data-width="350" data-height="86" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Radical_hyperconjugation.svg/525px-Radical_hyperconjugation.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e8/Radical_hyperconjugation.svg/700px-Radical_hyperconjugation.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>The relative stabilities of tertiary, secondary, primary and methyl radicals can be explained by hyperconjugation</figcaption></figure> <div class="mw-heading mw-heading4"><h4 id="Steric_hindrance">Steric hindrance</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=13" title="Edit section: Steric hindrance" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:N-hydroxypiperidine_Radical_Form.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/N-hydroxypiperidine_Radical_Form.svg/90px-N-hydroxypiperidine_Radical_Form.svg.png" decoding="async" width="90" height="171" class="mw-file-element" data-file-width="40" data-file-height="76"></noscript><span class="lazy-image-placeholder" style="width: 90px;height: 171px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/N-hydroxypiperidine_Radical_Form.svg/90px-N-hydroxypiperidine_Radical_Form.svg.png" data-width="90" data-height="171" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/N-hydroxypiperidine_Radical_Form.svg/135px-N-hydroxypiperidine_Radical_Form.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1e/N-hydroxypiperidine_Radical_Form.svg/180px-N-hydroxypiperidine_Radical_Form.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Radical form of <a href="/wiki/N-Hydroxypiperidine" title="N-Hydroxypiperidine"><i>N</i>-hydroxypiperidine</a></figcaption></figure> <p>Most simply, the greater the steric hindrance the more difficult it is for reactions to take place, and the radical form is favored by default. For example, compare the hydrogen-abstracted form of <a href="/wiki/N-Hydroxypiperidine" title="N-Hydroxypiperidine"><i>N</i>-hydroxypiperidine</a> to the molecule <a href="/wiki/TEMPO" title="TEMPO">TEMPO</a>.<sup id="cite_ref-:1_3-2" class="reference"><a href="#cite_note-:1-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> TEMPO, or (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl, is too sterically hindered by the additional methyl groups to react making it stable enough to be sold commercially in its radical form. <i>N</i>-Hydroxypiperidine, however, does not have the four methyl groups to impede the way of a reacting molecule so the structure is unstable.<sup id="cite_ref-:1_3-3" class="reference"><a href="#cite_note-:1-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading4"><h4 id="Facile_H-atom_donors">Facile H-atom donors</h4><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=14" title="Edit section: Facile H-atom donors" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p>The stability of many (or most) organic radicals is not indicated by their isolability but is manifested in their ability to function as donors of H<sup>•</sup>. This property reflects a weakened bond to hydrogen, usually O−H but sometimes N−H or C−H. This behavior is important because these H<sup>•</sup> donors serve as antioxidants in biology and in commerce. Illustrative is <a href="/wiki/Tocopherol" title="Tocopherol">α-tocopherol</a> (<a href="/wiki/Vitamin_E" title="Vitamin E">vitamin E</a>). The tocopherol radical itself is insufficiently stable for isolation, but the parent molecule is a highly effective hydrogen-atom donor. The C−H bond is weakened in <a href="/wiki/Triphenylmethyl" class="mw-redirect" title="Triphenylmethyl">triphenylmethyl</a> (trityl) derivatives. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:2,2,6,6-Tetramethylpiperidinyloxyl.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg/240px-2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg.png" decoding="async" width="240" height="150" class="mw-file-element" data-file-width="217" data-file-height="136"></noscript><span class="lazy-image-placeholder" style="width: 240px;height: 150px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg/240px-2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg.png" data-width="240" data-height="150" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg/360px-2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5c/2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg/480px-2%2C2%2C6%2C6-Tetramethylpiperidinyloxyl.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption><a href="/wiki/TEMPO" title="TEMPO">2,2,6,6-Tetramethylpiperidinyloxyl</a> is an example of a robust organic radical.</figcaption></figure> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(3)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Inorganic_radicals">Inorganic radicals</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=15" title="Edit section: Inorganic radicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-3 collapsible-block" id="mf-section-3"> <p>A large variety of inorganic radicals are stable and in fact isolable. Examples include most first-row transition metal complexes. </p><p>With regard to main group radicals, the most abundant radical in the universe is also the most abundant chemical in the universe, H<sup>•</sup>. Most main group radicals are not however <i>isolable</i>, despite their intrinsic stability. Hydrogen radicals for example combine eagerly to form H<sub>2</sub>. <a href="/wiki/Nitric_oxide" title="Nitric oxide">Nitric oxide</a> (NO) is well known example of an isolable inorganic radical. <a href="/wiki/Fremy%27s_salt" class="mw-redirect" title="Fremy's salt">Fremy's salt</a> (Potassium nitrosodisulfonate, (KSO<sub>3</sub>)<sub>2</sub>NO) is a related example. Many <a href="/wiki/Sulfur_mononitride" title="Sulfur mononitride">thiazyl</a> radicals are known, despite limited extent of π <a href="/wiki/Resonance_stabilization" class="mw-redirect" title="Resonance stabilization">resonance stabilization</a>.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> </p><p>Many radicals can be envisioned as the products of <a href="/wiki/Bond_cleavage" title="Bond cleavage">breaking of covalent bonds</a> by <a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">homolysis</a>. The homolytic <a href="/wiki/Bond_dissociation_energy" class="mw-redirect" title="Bond dissociation energy">bond dissociation energies</a>, usually abbreviated as "Δ<i>H</i> °" are a measure of bond strength. Splitting H<sub>2</sub> into 2 H<sup>•</sup>, for example, requires a Δ<i>H</i> ° of +435 <a href="/wiki/Joule_per_mole" title="Joule per mole">kJ/mol</a>, while splitting Cl<sub>2</sub> into two Cl<sup>•</sup> requires a Δ<i>H</i> ° of +243 kJ/mol. For weak bonds, homolysis can be induced thermally. Strong bonds require high energy photons or even flames to induce homolysis. </p> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(4)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Diradicals">Diradicals</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=16" title="Edit section: Diradicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-4 collapsible-block" id="mf-section-4"> <p><a href="/wiki/Diradical" title="Diradical">Diradicals</a> are molecules containing two radical centers. <a href="/wiki/Dioxygen" class="mw-redirect" title="Dioxygen">Dioxygen</a> (O<sub>2</sub>) is an important example of a stable diradical. <a href="/wiki/Singlet_oxygen" title="Singlet oxygen">Singlet oxygen</a>, the lowest-energy non-radical state of dioxygen, is less stable than the diradical due to <a href="/wiki/Hund%27s_rule_of_maximum_multiplicity" title="Hund's rule of maximum multiplicity">Hund's rule of maximum multiplicity</a>. The relative stability of the oxygen diradical is primarily due to the <a href="/wiki/Quantum_chemistry" title="Quantum chemistry">spin-forbidden</a> nature of the triplet-singlet transition required for it to grab electrons, i.e., "<b>oxidize</b>". The diradical state of oxygen also results in its paramagnetic character, which is demonstrated by its attraction to an external magnet.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Diradicals can also occur in <a href="/wiki/Transition_metal_oxo_complex" title="Transition metal oxo complex">metal-oxo complexes</a>, lending themselves for studies of <a href="/wiki/Spin_forbidden_reactions" class="mw-redirect" title="Spin forbidden reactions">spin forbidden reactions</a> in <a href="/wiki/Transition_metal" title="Transition metal">transition metal</a> chemistry.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Carbene" title="Carbene">Carbenes</a> in their triplet state can be viewed as diradicals centred on the same atom, while these are usually highly reactive <a href="/wiki/Persistent_carbene" title="Persistent carbene">persistent carbenes</a> are known, with N-heterocyclic carbenes being the most common example. </p><p>Triplet <a href="/wiki/Carbene" title="Carbene">carbenes</a> and <a href="/wiki/Nitrene" title="Nitrene">nitrenes</a> are diradicals. Their chemical properties are distinct from the properties of their singlet analogues. </p> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(5)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Occurrence_of_radicals">Occurrence of radicals</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=17" title="Edit section: Occurrence of radicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-5 collapsible-block" id="mf-section-5"> <div class="mw-heading mw-heading3"><h3 id="Combustion">Combustion</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=18" title="Edit section: Combustion" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Spectrum_of_blue_flame.png" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/en/thumb/b/b2/Spectrum_of_blue_flame.png/330px-Spectrum_of_blue_flame.png" decoding="async" width="330" height="229" class="mw-file-element" data-file-width="3950" data-file-height="2739"></noscript><span class="lazy-image-placeholder" style="width: 330px;height: 229px;" data-src="//upload.wikimedia.org/wikipedia/en/thumb/b/b2/Spectrum_of_blue_flame.png/330px-Spectrum_of_blue_flame.png" data-width="330" data-height="229" data-srcset="//upload.wikimedia.org/wikipedia/en/thumb/b/b2/Spectrum_of_blue_flame.png/495px-Spectrum_of_blue_flame.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/b/b2/Spectrum_of_blue_flame.png/660px-Spectrum_of_blue_flame.png 2x" data-class="mw-file-element"> </span></a><figcaption>Spectrum of the blue flame from a <a href="/wiki/Butane" title="Butane">butane</a> torch showing excited molecular radical band emission and <a href="/wiki/Swan_bands" class="mw-redirect" title="Swan bands">Swan bands</a></figcaption></figure> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Combustion#Reaction_mechanism" title="Combustion">Combustion § Reaction mechanism</a></div> <p>A familiar radical reaction is <a href="/wiki/Combustion" title="Combustion">combustion</a>. The <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> molecule is a stable <a href="/wiki/Diradical" title="Diradical">diradical</a>, best represented by <sup>•</sup>O–O<sup>•</sup>. Because <a href="/wiki/Spin_(physics)" title="Spin (physics)">spins</a> of the electrons are parallel, this molecule is stable. While the <a href="/wiki/Ground_state" title="Ground state">ground state</a> of oxygen is this unreactive spin-unpaired (<a href="/wiki/Triplet_oxygen" title="Triplet oxygen">triplet</a>) diradical, an extremely reactive spin-paired (<a href="/wiki/Singlet_oxygen" title="Singlet oxygen">singlet</a>) state is available. For combustion to occur, the <a href="/wiki/Energy_barrier" class="mw-redirect" title="Energy barrier">energy barrier</a> between these must be overcome. This barrier can be overcome by heat, requiring high temperatures. The triplet-singlet transition is also "<a href="/wiki/Forbidden_mechanism" title="Forbidden mechanism">forbidden</a>". This presents an additional barrier to the reaction. It also means molecular oxygen is relatively unreactive at room temperature except in the presence of a catalytic heavy atom such as iron or copper. </p><p>Combustion consists of various radical chain reactions that the singlet radical can initiate. The <a href="/wiki/Flammability" class="mw-redirect" title="Flammability">flammability</a> of a given material strongly depends on the concentration of radicals that must be obtained before initiation and propagation reactions dominate leading to <a href="/wiki/Combustion" title="Combustion">combustion</a> of the material. Once the combustible material has been consumed, termination reactions again dominate and the flame dies out. As indicated, promotion of propagation or termination reactions alters flammability. For example, because lead itself deactivates radicals in the gasoline-air mixture, <a href="/wiki/Tetraethyl_lead" class="mw-redirect" title="Tetraethyl lead">tetraethyl lead</a> was once commonly added to gasoline. This prevents the combustion from initiating in an uncontrolled manner or in unburnt residues (<a href="/wiki/Engine_knocking" title="Engine knocking">engine knocking</a>) or premature ignition (<a href="/wiki/Preignition" class="mw-redirect" title="Preignition">preignition</a>). </p><p>When a hydrocarbon is burned, a large number of different oxygen radicals are involved. Initially, <a href="/wiki/Hydroperoxyl" title="Hydroperoxyl">hydroperoxyl radical</a> (HOO<sup>•</sup>) are formed. These then react further to give <a href="/wiki/Organic_hydroperoxide" class="mw-redirect" title="Organic hydroperoxide">organic hydroperoxides</a> that break up into <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radicals</a> (HO<sup>•</sup>). </p> <div class="mw-heading mw-heading3"><h3 id="Polymerization">Polymerization</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=19" title="Edit section: Polymerization" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p>Many <a href="/wiki/Polymerization" title="Polymerization">polymerization</a> reactions are initiated by radicals. Polymerization involves an initial radical adding to non-radical (usually an alkene) to give new radicals. This process is the basis of the <a href="/w/index.php?title=Radical_chain_reaction&action=edit&redlink=1" class="new" title="Radical chain reaction (page does not exist)">radical chain reaction</a>. The art of polymerization entails the method by which the initiating radical is introduced. For example, <a href="/wiki/Methyl_methacrylate" title="Methyl methacrylate">methyl methacrylate</a> (MMA) can be polymerized to produce <a href="/wiki/Poly(methyl_methacrylate)" title="Poly(methyl methacrylate)">Poly(methyl methacrylate)</a> (PMMA – Plexiglas or Perspex) via a repeating series of <a href="/wiki/Free-radical_addition" title="Free-radical addition">radical addition</a> steps: </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:PMMA-Wachstum.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/03/PMMA-Wachstum.svg/740px-PMMA-Wachstum.svg.png" decoding="async" width="740" height="107" class="mw-file-element" data-file-width="1342" data-file-height="194"></noscript><span class="lazy-image-placeholder" style="width: 740px;height: 107px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/0/03/PMMA-Wachstum.svg/740px-PMMA-Wachstum.svg.png" data-width="740" data-height="107" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/03/PMMA-Wachstum.svg/1110px-PMMA-Wachstum.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/03/PMMA-Wachstum.svg/1480px-PMMA-Wachstum.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Radical intermediates in the formation of polymethacrylate (plexiglas or perspex)</figcaption></figure> <p>Newer radical polymerization methods are known as <a href="/wiki/Living_polymerization" title="Living polymerization">living radical polymerization</a>. Variants include reversible addition-fragmentation chain transfer (<a href="/wiki/RAFT_(chemistry)" class="mw-redirect" title="RAFT (chemistry)">RAFT</a>) and atom transfer radical polymerization (<a href="/wiki/ATRP_(chemistry)" class="mw-redirect" title="ATRP (chemistry)">ATRP</a>). </p><p>Being a prevalent radical, O<sub>2</sub> reacts with many organic compounds to generate radicals together with the <a href="/wiki/Hydroperoxide" title="Hydroperoxide">hydroperoxide</a> radical. <a href="/wiki/Drying_oil" title="Drying oil">Drying oils</a> and alkyd paints harden due to radical crosslinking initiated by oxygen from the atmosphere. </p> <div class="mw-heading mw-heading3"><h3 id="Atmospheric_radicals">Atmospheric radicals</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=20" title="Edit section: Atmospheric radicals" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Oxygen_cycle" title="Oxygen cycle">Oxygen cycle</a> and <a href="/wiki/Ozone-oxygen_cycle" class="mw-redirect" title="Ozone-oxygen cycle">Ozone-oxygen cycle</a></div> <p>The most common radical in the lower atmosphere is molecular dioxygen. <a href="/wiki/Photodissociation" title="Photodissociation">Photodissociation</a> of source molecules produces other radicals. In the lower atmosphere, important radical are produced by the photodissociation of <a href="/wiki/Nitrogen_dioxide" title="Nitrogen dioxide">nitrogen dioxide</a> to an oxygen atom and <a href="/wiki/Nitric_oxide" title="Nitric oxide">nitric oxide</a> (see <b><a href="#math_eq._1.1">eq. 1.1</a></b> below), which plays a key role in <a href="/wiki/Photochemical_smog" class="mw-redirect" title="Photochemical smog">smog</a> formation—and the photodissociation of ozone to give the excited oxygen atom O(1D) (see <b><a href="#math_eq._1.2">eq. 1.2</a></b> below). The net and return reactions are also shown (<b><a href="#math_eq._1.3">eq. 1.3</a></b> and <b><a href="#math_eq._1.4">eq. 1.4</a></b>, respectively). </p> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {NO2 ->[h \nu] NO + O}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <msubsup> <mtext>NO</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mrow class="MJX-TeXAtom-REL"> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>h</mi> <mi>ν</mi> </mpadded> </mover> </mrow> <mtext>NO</mtext> <mo>+</mo> <mtext>O</mtext> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {NO2 ->[h \nu] NO + O}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/5da627b27ee3e5b4dc45b156c54a91e1d79ffbd1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; margin-top: -0.311ex; width:17.237ex; height:4.343ex;" alt="{\displaystyle {\ce {NO2 ->[h \nu] NO + O}}}"></noscript><span class="lazy-image-placeholder" style="width: 17.237ex;height: 4.343ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/5da627b27ee3e5b4dc45b156c54a91e1d79ffbd1" data-alt="{\displaystyle {\ce {NO2 ->[h \nu] NO + O}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._1.1" class="reference nourlexpansion" style="font-weight:bold;">eq. 1.1</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {O + O2 -> O3}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>O</mtext> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mo stretchy="false">⟶</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {O + O2 -> O3}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/42d7c91ba2c43510408c3018ea096a9dff936d00" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:15.469ex; height:2.843ex;" alt="{\displaystyle {\ce {O + O2 -> O3}}}"></noscript><span class="lazy-image-placeholder" style="width: 15.469ex;height: 2.843ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/42d7c91ba2c43510408c3018ea096a9dff936d00" data-alt="{\displaystyle {\ce {O + O2 -> O3}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._1.2" class="reference nourlexpansion" style="font-weight:bold;">eq. 1.2</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {NO2 + O2 ->[h \nu] NO + O3}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <msubsup> <mtext>NO</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mrow class="MJX-TeXAtom-REL"> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>h</mi> <mi>ν</mi> </mpadded> </mover> </mrow> <mtext>NO</mtext> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {NO2 + O2 ->[h \nu] NO + O3}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/eae7fc4c91c01822b8db1423a88911a1eb56a171" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; margin-top: -0.311ex; width:23.994ex; height:4.343ex;" alt="{\displaystyle {\ce {NO2 + O2 ->[h \nu] NO + O3}}}"></noscript><span class="lazy-image-placeholder" style="width: 23.994ex;height: 4.343ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/eae7fc4c91c01822b8db1423a88911a1eb56a171" data-alt="{\displaystyle {\ce {NO2 + O2 ->[h \nu] NO + O3}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._1.3" class="reference nourlexpansion" style="font-weight:bold;">eq. 1.3</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {NO + O3 -> NO2 + O2}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>NO</mtext> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mo stretchy="false">⟶</mo> <msubsup> <mtext>NO</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {NO + O3 -> NO2 + O2}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0544e0d0f68112d969a60168581b41199aa642b7" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:24.658ex; height:2.843ex;" alt="{\displaystyle {\ce {NO + O3 -> NO2 + O2}}}"></noscript><span class="lazy-image-placeholder" style="width: 24.658ex;height: 2.843ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0544e0d0f68112d969a60168581b41199aa642b7" data-alt="{\displaystyle {\ce {NO + O3 -> NO2 + O2}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._1.4" class="reference nourlexpansion" style="font-weight:bold;">eq. 1.4</span>)</b></td></tr></tbody></table> <p>In the upper atmosphere, the photodissociation of normally unreactive <a href="/wiki/Chlorofluorocarbon" title="Chlorofluorocarbon">chlorofluorocarbons</a> (CFCs) by solar <a href="/wiki/Ultraviolet_radiation" class="mw-redirect" title="Ultraviolet radiation">ultraviolet radiation</a> is an important source of radicals (see eq. 1 below). These reactions give the <a href="/wiki/Chlorine" title="Chlorine">chlorine</a> radical, Cl<sup>•</sup>, which catalyzes the conversion of <a href="/wiki/Ozone" title="Ozone">ozone</a> to O<sub>2</sub>, thus facilitating <a href="/wiki/Ozone_depletion" title="Ozone depletion">ozone depletion</a> (<b><a href="#math_eq._2.2">eq. 2.2</a></b>–<b><a href="#math_eq._2.4">eq. 2.4</a></b> below). </p> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {CFCS->[h\nu ]Cl^{\bullet }}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>CFCS</mtext> <mrow class="MJX-TeXAtom-REL"> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>h</mi> <mi>ν</mi> </mpadded> </mover> </mrow> <msup> <mtext>Cl</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {CFCS->[h\nu ]Cl^{\bullet }}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8bdfdc999e29261e922e3863cdfa3b4bf84fb5a2" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.053ex; margin-top: -0.311ex; margin-bottom: -0.451ex; width:13.978ex; height:3.843ex;" alt="{\displaystyle {\ce {CFCS->[h\nu ]Cl^{\bullet }}}}"></noscript><span class="lazy-image-placeholder" style="width: 13.978ex;height: 3.843ex;vertical-align: -0.053ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/8bdfdc999e29261e922e3863cdfa3b4bf84fb5a2" data-alt="{\displaystyle {\ce {CFCS->[h\nu ]Cl^{\bullet }}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._2.1" class="reference nourlexpansion" style="font-weight:bold;">eq. 2.1</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {Cl^{\bullet }{}+O3->ClO^{\bullet }{}+O2}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mtext>Cl</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mo stretchy="false">⟶</mo> <msup> <mtext>ClO</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {Cl^{\bullet }{}+O3->ClO^{\bullet }{}+O2}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fa07f2a9383831fc6e1e76b5c68fc254e6d492f9" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:25.068ex; height:3.009ex;" alt="{\displaystyle {\ce {Cl^{\bullet }{}+O3->ClO^{\bullet }{}+O2}}}"></noscript><span class="lazy-image-placeholder" style="width: 25.068ex;height: 3.009ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/fa07f2a9383831fc6e1e76b5c68fc254e6d492f9" data-alt="{\displaystyle {\ce {Cl^{\bullet }{}+O3->ClO^{\bullet }{}+O2}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._2.2" class="reference nourlexpansion" style="font-weight:bold;">eq. 2.2</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {O3 ->[h \nu] O + O2}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mrow class="MJX-TeXAtom-REL"> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>h</mi> <mi>ν</mi> </mpadded> </mover> </mrow> <mtext>O</mtext> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {O3 ->[h \nu] O + O2}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3acd85b4a5f671e0a421576bf91c3352bec070c1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; margin-top: -0.311ex; width:14.805ex; height:4.343ex;" alt="{\displaystyle {\ce {O3 ->[h \nu] O + O2}}}"></noscript><span class="lazy-image-placeholder" style="width: 14.805ex;height: 4.343ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3acd85b4a5f671e0a421576bf91c3352bec070c1" data-alt="{\displaystyle {\ce {O3 ->[h \nu] O + O2}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._2.3" class="reference nourlexpansion" style="font-weight:bold;">eq. 2.3</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {O{}+ClO^{\bullet }->Cl^{\bullet }{}+O2}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mo>+</mo> <msup> <mtext>ClO</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> <mo stretchy="false">⟶</mo> <msup> <mtext>Cl</mtext> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mo>+</mo> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {O{}+ClO^{\bullet }->Cl^{\bullet }{}+O2}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1121aff72c85cf5088e882d39a6b503682da313a" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:24.014ex; height:3.009ex;" alt="{\displaystyle {\ce {O{}+ClO^{\bullet }->Cl^{\bullet }{}+O2}}}"></noscript><span class="lazy-image-placeholder" style="width: 24.014ex;height: 3.009ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/1121aff72c85cf5088e882d39a6b503682da313a" data-alt="{\displaystyle {\ce {O{}+ClO^{\bullet }->Cl^{\bullet }{}+O2}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._2.4" class="reference nourlexpansion" style="font-weight:bold;">eq. 2.4</span>)</b></td></tr></tbody></table> <table role="presentation" style="border-collapse:collapse; margin:0 0 0 1.6em; border:none;"><tbody><tr><td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\ce {2O3 ->[h \nu] 3O2}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> <mspace width="thinmathspace"></mspace> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> <mrow class="MJX-TeXAtom-REL"> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>h</mi> <mi>ν</mi> </mpadded> </mover> </mrow> <mn>3</mn> <mspace width="thinmathspace"></mspace> <msubsup> <mtext>O</mtext> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mspace width="0pt" height="0pt" depth=".2em"></mspace> </mrow> </msubsup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\ce {2O3 ->[h \nu] 3O2}}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/afc621f0abb1c9cfc08b3cf82f43d9fc60a29c40" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; margin-top: -0.311ex; width:13.256ex; height:4.343ex;" alt="{\displaystyle {\ce {2O3 ->[h \nu] 3O2}}}"></noscript><span class="lazy-image-placeholder" style="width: 13.256ex;height: 4.343ex;vertical-align: -1.005ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/afc621f0abb1c9cfc08b3cf82f43d9fc60a29c40" data-alt="{\displaystyle {\ce {2O3 ->[h \nu] 3O2}}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></td> <td style="vertical-align:middle; width:99%; border:none; padding:0;"></td> <td style="vertical-align:middle; border:none; padding:0;" class="nowrap"><b>(<span id="math_eq._2.5" class="reference nourlexpansion" style="font-weight:bold;">eq. 2.5</span>)</b></td></tr></tbody></table> <p>Such reactions cause the depletion of the <a href="/wiki/Ozone_layer" title="Ozone layer">ozone layer</a>, especially since the chlorine radical is free to engage in another reaction chain; consequently, the use of chlorofluorocarbons as <a href="/wiki/Refrigerant" title="Refrigerant">refrigerants</a> has been restricted. </p> <div class="mw-heading mw-heading3"><h3 id="In_biology">In biology</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=21" title="Edit section: In biology" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Dioxygen_in_biological_reactions" title="Dioxygen in biological reactions">Dioxygen in biological reactions</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:DeoxyadenosylRadical.png" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/DeoxyadenosylRadical.png/220px-DeoxyadenosylRadical.png" decoding="async" width="220" height="214" class="mw-file-element" data-file-width="969" data-file-height="941"></noscript><span class="lazy-image-placeholder" style="width: 220px;height: 214px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/DeoxyadenosylRadical.png/220px-DeoxyadenosylRadical.png" data-width="220" data-height="214" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/66/DeoxyadenosylRadical.png/330px-DeoxyadenosylRadical.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/66/DeoxyadenosylRadical.png/440px-DeoxyadenosylRadical.png 2x" data-class="mw-file-element"> </span></a><figcaption>Structure of the <a href="/wiki/Deoxyadenosyl_radical" title="Deoxyadenosyl radical">deoxyadenosyl radical</a>, a common biosynthetic intermediate<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup></figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Lignin_structure.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Lignin_structure.svg/500px-Lignin_structure.svg.png" decoding="async" width="500" height="483" class="mw-file-element" data-file-width="1470" data-file-height="1420"></noscript><span class="lazy-image-placeholder" style="width: 500px;height: 483px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Lignin_structure.svg/500px-Lignin_structure.svg.png" data-width="500" data-height="483" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Lignin_structure.svg/750px-Lignin_structure.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Lignin_structure.svg/1000px-Lignin_structure.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>An approximate structure of <a href="/wiki/Lignin" title="Lignin">lignin</a>, which constitutes about 30% of plant matter. It is formed by radical reactions.</figcaption></figure> <p>Radicals play important roles in biology. Many of these are necessary for life, such as the intracellular killing of bacteria by phagocytic cells such as <a href="/wiki/Granulocyte" title="Granulocyte">granulocytes</a> and <a href="/wiki/Macrophage" title="Macrophage">macrophages</a>. Radicals are involved in <a href="/wiki/Signal_transduction" title="Signal transduction">cell signalling</a> processes,<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> known as <a href="/wiki/Redox_signaling" class="mw-redirect" title="Redox signaling">redox signaling</a>. For example, radical attack of <a href="/wiki/Linoleic_acid" title="Linoleic acid">linoleic acid</a> produces a series of <a href="/wiki/13-hydroxyoctadecadienoic_acid" class="mw-redirect" title="13-hydroxyoctadecadienoic acid">13-hydroxyoctadecadienoic acids</a> and <a href="/wiki/9-hydroxyoctadecadienoic_acid" class="mw-redirect" title="9-hydroxyoctadecadienoic acid">9-hydroxyoctadecadienoic acids</a>, which may act to regulate localized tissue inflammatory and/or healing responses, pain perception, and the proliferation of malignant cells. Radical attacks on arachidonic acid and docosahexaenoic acid produce a similar but broader array of signaling products.<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p><p>Radicals may also be involved in <a href="/wiki/Parkinson%27s_disease" title="Parkinson's disease">Parkinson's disease</a>, senile and drug-induced <a href="/wiki/Deafness" title="Deafness">deafness</a>, <a href="/wiki/Schizophrenia" title="Schizophrenia">schizophrenia</a>, and <a href="/wiki/Alzheimer%27s" class="mw-redirect" title="Alzheimer's">Alzheimer's</a>.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> The classic free-radical syndrome, the iron-storage disease <a href="/wiki/Hemochromatosis" class="mw-redirect" title="Hemochromatosis">hemochromatosis</a>, is typically associated with a constellation of free-radical-related symptoms including movement disorder, psychosis, skin pigmentary <a href="/wiki/Melanin" title="Melanin">melanin</a> abnormalities, deafness, arthritis, and diabetes mellitus. The <a href="/wiki/Free-radical_theory" class="mw-redirect" title="Free-radical theory">free-radical theory</a> of aging proposes that radicals underlie the <a href="/wiki/Senescence" title="Senescence">aging process</a> itself. Similarly, the process of mito<a href="/wiki/Hormesis" title="Hormesis">hormesis</a> suggests that repeated exposure to radicals may extend life span. </p><p>Because radicals are necessary for life, the body has a number of mechanisms to minimize radical-induced damage and to repair damage that occurs, such as the <a href="/wiki/Enzyme" title="Enzyme">enzymes</a> <a href="/wiki/Superoxide_dismutase" title="Superoxide dismutase">superoxide dismutase</a>, <a href="/wiki/Catalase" title="Catalase">catalase</a>, <a href="/wiki/Glutathione_peroxidase" title="Glutathione peroxidase">glutathione peroxidase</a> and <a href="/wiki/Glutathione_reductase" title="Glutathione reductase">glutathione reductase</a>. In addition, <a href="/wiki/Antioxidant" title="Antioxidant">antioxidants</a> play a key role in these defense mechanisms. These are often the three vitamins, <a href="/wiki/Vitamin_A" title="Vitamin A">vitamin A</a>, <a href="/wiki/Vitamin_C" title="Vitamin C">vitamin C</a> and <a href="/wiki/Vitamin_E" title="Vitamin E">vitamin E</a> and <a href="/wiki/Polyphenol_antioxidant" class="mw-redirect" title="Polyphenol antioxidant">polyphenol antioxidants</a>. Furthermore, there is good evidence indicating that <a href="/wiki/Bilirubin" title="Bilirubin">bilirubin</a> and <a href="/wiki/Uric_acid" title="Uric acid">uric acid</a> can act as antioxidants to help neutralize certain radicals. Bilirubin comes from the breakdown of <a href="/wiki/Red_blood_cell" title="Red blood cell">red blood cells</a>' contents, while uric acid is a breakdown product of <a href="/wiki/Purine" title="Purine">purines</a>. Too much bilirubin, though, can lead to <a href="/wiki/Jaundice" title="Jaundice">jaundice</a>, which could eventually damage the central nervous system, while too much uric acid causes <a href="/wiki/Gout" title="Gout">gout</a>.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Reactive_oxygen_species">Reactive oxygen species</h3><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=22" title="Edit section: Reactive oxygen species" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div> <p><a href="/wiki/Reactive_oxygen_species" title="Reactive oxygen species">Reactive oxygen species</a> or ROS are species such as <a href="/wiki/Superoxide" title="Superoxide">superoxide</a>, <a href="/wiki/Hydrogen_peroxide" title="Hydrogen peroxide">hydrogen peroxide</a>, and <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radical</a>, commonly associated with cell damage. ROS form as a natural by-product of the normal metabolism of <a href="/wiki/Oxygen" title="Oxygen">oxygen</a> and have important roles in cell signaling. Two important oxygen-centered radicals are <a href="/wiki/Superoxide" title="Superoxide">superoxide</a> and <a href="/wiki/Hydroxyl_radical" title="Hydroxyl radical">hydroxyl radical</a>. They derive from molecular oxygen under reducing conditions. However, because of their reactivity, these same radicals can participate in unwanted side reactions resulting in cell damage. Excessive amounts of these radicals can lead to cell injury and <a href="/wiki/Death" title="Death">death</a>, which may contribute to many diseases such as <a href="/wiki/Cancer" title="Cancer">cancer</a>, <a href="/wiki/Stroke" title="Stroke">stroke</a>, <a href="/wiki/Myocardial_infarction" title="Myocardial infarction">myocardial infarction</a>, <a href="/wiki/Diabetes" title="Diabetes">diabetes</a> and major disorders.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> Many forms of <a href="/wiki/Cancer" title="Cancer">cancer</a> are thought to be the result of reactions between radicals and <a href="/wiki/DNA" title="DNA">DNA</a>, potentially resulting in <a href="/wiki/Mutation" title="Mutation">mutations</a> that can adversely affect the <a href="/wiki/Cell_cycle" title="Cell cycle">cell cycle</a> and potentially lead to malignancy.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> Some of the symptoms of <a href="/wiki/Senescence" title="Senescence">aging</a> such as <a href="/wiki/Atherosclerosis" title="Atherosclerosis">atherosclerosis</a> are also attributed to radical induced oxidation of cholesterol to 7-ketocholesterol.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> In addition radicals contribute to <a href="/wiki/Alcohol_(drug)" title="Alcohol (drug)">alcohol</a>-induced <a href="/wiki/Liver" title="Liver">liver</a> damage, perhaps more than alcohol itself. Radicals produced by <a href="/wiki/Cigarette" title="Cigarette">cigarette</a> <a href="/wiki/Smoke" title="Smoke">smoke</a> are implicated in inactivation of <a href="/wiki/Alpha_1-antitrypsin" class="mw-redirect" title="Alpha 1-antitrypsin">alpha 1-antitrypsin</a> in the <a href="/wiki/Lung" title="Lung">lung</a>. This process promotes the development of <a href="/wiki/Emphysema" title="Emphysema">emphysema</a>. </p><p><a href="/wiki/Oxybenzone" title="Oxybenzone">Oxybenzone</a> has been found to form radicals in sunlight, and therefore may be associated with cell damage as well. This only occurred when it was combined with other ingredients commonly found in sunscreens, like <a href="/wiki/Titanium_oxide" title="Titanium oxide">titanium oxide</a> and <a href="/wiki/Octyl_methoxycinnamate" title="Octyl methoxycinnamate">octyl methoxycinnamate</a>.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> </p><p>ROS attack the <a href="/wiki/Polyunsaturated_fatty_acid" class="mw-redirect" title="Polyunsaturated fatty acid">polyunsaturated fatty acid</a>, <a href="/wiki/Linoleic_acid" title="Linoleic acid">linoleic acid</a>, to form a series of <a href="/wiki/13-hydroxyoctadecadienoic_acid" class="mw-redirect" title="13-hydroxyoctadecadienoic acid">13-hydroxyoctadecadienoic acid</a> and <a href="/wiki/9-hydroxyoctadecadienoic_acid" class="mw-redirect" title="9-hydroxyoctadecadienoic acid">9-hydroxyoctadecadienoic acid</a> products that serve as signaling molecules that may trigger responses that counter the tissue injury which caused their formation. ROS attacks other polyunsaturated fatty acids, e.g. <a href="/wiki/Arachidonic_acid" title="Arachidonic acid">arachidonic acid</a> and <a href="/wiki/Docosahexaenoic_acid" title="Docosahexaenoic acid">docosahexaenoic acid</a>, to produce a similar series of signaling products.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> </p><p>Reactive oxygen species are also used in controlled reactions involving singlet dioxygen <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {}^{1}\mathrm {O} _{2}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>1</mn> </mrow> </msup> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">O</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {}^{1}\mathrm {O} _{2}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/02c4b0b1b121b660391be3b3a6fc8b78603384b6" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:3.917ex; height:3.009ex;" alt="{\displaystyle {}^{1}\mathrm {O} _{2}}"></noscript><span class="lazy-image-placeholder" style="width: 3.917ex;height: 3.009ex;vertical-align: -0.671ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/02c4b0b1b121b660391be3b3a6fc8b78603384b6" data-alt="{\displaystyle {}^{1}\mathrm {O} _{2}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span> known as type II <a href="/wiki/Photooxygenation" title="Photooxygenation">photooxygenation</a> reactions after <a href="/wiki/Dexter_electron_transfer" title="Dexter electron transfer">Dexter</a> energy transfer (<a href="/wiki/Triplet-triplet_annihilation" title="Triplet-triplet annihilation">triplet-triplet annihilation</a>) from natural triplet dioxygen <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {}^{3}\mathrm {O} _{2}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msup> <mrow class="MJX-TeXAtom-ORD"> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msup> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">O</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {}^{3}\mathrm {O} _{2}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/46a6a988aac15367bcdc6295a30034fbef7067b4" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:3.917ex; height:3.009ex;" alt="{\displaystyle {}^{3}\mathrm {O} _{2}}"></noscript><span class="lazy-image-placeholder" style="width: 3.917ex;height: 3.009ex;vertical-align: -0.671ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/46a6a988aac15367bcdc6295a30034fbef7067b4" data-alt="{\displaystyle {}^{3}\mathrm {O} _{2}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span> and triplet excited state of a photosensitizer. Typical chemical transformations with this singlet dioxygen species involve, among others, conversion of cellulosic biowaste into new <a href="/wiki/Polymethine_dyes" title="Polymethine dyes">poylmethine</a> dyes.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> </p> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(6)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="Depiction_in_chemical_reactions">Depiction in chemical reactions</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=23" title="Edit section: Depiction in chemical reactions" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-6 collapsible-block" id="mf-section-6"> <p>In chemical equations, radicals are frequently denoted by a dot placed immediately to the right of the atomic symbol or molecular formula as follows: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {Cl} _{2}\;\xrightarrow {UV} \;2{\mathrm {Cl} ^{\bullet }}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">C</mi> <mi mathvariant="normal">l</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msub> <mspace width="thickmathspace"></mspace> <mover> <mo>→</mo> <mpadded width="+0.611em" lspace="0.278em" voffset=".15em"> <mi>U</mi> <mi>V</mi> </mpadded> </mover> <mspace width="thickmathspace"></mspace> <mn>2</mn> <mrow class="MJX-TeXAtom-ORD"> <msup> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">C</mi> <mi mathvariant="normal">l</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>∙</mo> </mrow> </msup> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {Cl} _{2}\;\xrightarrow {UV} \;2{\mathrm {Cl} ^{\bullet }}}</annotation> </semantics> </math></span><noscript><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/bd1b83e5ce1b2a31d5d04e859a5fda181ed517f1" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; margin-top: -0.329ex; width:14.349ex; height:4.009ex;" alt="{\displaystyle \mathrm {Cl} _{2}\;\xrightarrow {UV} \;2{\mathrm {Cl} ^{\bullet }}}"></noscript><span class="lazy-image-placeholder" style="width: 14.349ex;height: 4.009ex;vertical-align: -0.671ex;" data-src="https://wikimedia.org/api/rest_v1/media/math/render/svg/bd1b83e5ce1b2a31d5d04e859a5fda181ed517f1" data-alt="{\displaystyle \mathrm {Cl} _{2}\;\xrightarrow {UV} \;2{\mathrm {Cl} ^{\bullet }}}" data-class="mwe-math-fallback-image-inline mw-invert skin-invert"> </span></span></dd></dl> <p>Radical <a href="/wiki/Reaction_mechanism" title="Reaction mechanism">reaction mechanisms</a> use single-headed arrows to depict the movement of single electrons: </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Internal_radical.svg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Internal_radical.svg/400px-Internal_radical.svg.png" decoding="async" width="400" height="98" class="mw-file-element" data-file-width="171" data-file-height="42"></noscript><span class="lazy-image-placeholder" style="width: 400px;height: 98px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Internal_radical.svg/400px-Internal_radical.svg.png" data-width="400" data-height="98" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Internal_radical.svg/600px-Internal_radical.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/ae/Internal_radical.svg/800px-Internal_radical.svg.png 2x" data-class="mw-file-element"> </span></a><figcaption>Example of an arrow-pushing mechanism for an internal radical reaction.</figcaption></figure> <p>The <a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">homolytic</a> cleavage of the breaking bond is drawn with a "fish-hook" arrow to distinguish from the usual movement of two electrons depicted by a standard curly arrow. The second electron of the breaking bond also moves to pair up with the attacking radical electron. </p><p>Radicals also take part in <a href="/wiki/Radical_addition" class="mw-redirect" title="Radical addition">radical addition</a> and <a href="/wiki/Radical_substitution" title="Radical substitution">radical substitution</a> as <a href="/wiki/Reactive_intermediate" title="Reactive intermediate">reactive intermediates</a>. <a href="/wiki/Chain_reaction#Chemical_chain_reactions" title="Chain reaction">Chain reactions</a> involving radicals can usually be divided into three distinct processes. These are <i>initiation</i>, <i>propagation</i>, and <i>termination</i>. </p> <ul><li><i>Initiation</i> reactions are those that result in a net increase in the number of radicals. They may involve the formation of radicals from stable species as in Reaction 1 above or they may involve reactions of radicals with stable species to form more radicals.</li> <li><i>Propagation</i> reactions are those reactions involving radicals in which the total number of radicals remains the same.</li> <li><i>Termination</i> reactions are those reactions resulting in a net decrease in the number of radicals. Typically two radicals combine to form a more stable species, for example: <dl><dd>2 Cl<sup>•</sup> → Cl<sub>2</sub></dd></dl></li></ul> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(7)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="History_and_nomenclature">History and nomenclature</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=24" title="Edit section: History and nomenclature" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-7 collapsible-block" id="mf-section-7"> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Gombergm01.jpg" class="mw-file-description"><noscript><img src="//upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Gombergm01.jpg/170px-Gombergm01.jpg" decoding="async" width="170" height="247" class="mw-file-element" data-file-width="275" data-file-height="400"></noscript><span class="lazy-image-placeholder" style="width: 170px;height: 247px;" data-src="//upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Gombergm01.jpg/170px-Gombergm01.jpg" data-width="170" data-height="247" data-srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/cd/Gombergm01.jpg/255px-Gombergm01.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/c/cd/Gombergm01.jpg 2x" data-class="mw-file-element"> </span></a><figcaption><a href="/wiki/Moses_Gomberg" title="Moses Gomberg">Moses Gomberg</a> (1866–1947), the founder of radical chemistry</figcaption></figure> <p>Until late in the 20th century the word "radical" was used in chemistry to indicate any connected group of atoms, such as a <a href="/wiki/Methyl" class="mw-redirect" title="Methyl">methyl group</a> or a <a href="/wiki/Carboxyl" class="mw-redirect" title="Carboxyl">carboxyl</a>, whether it was part of a larger molecule or a molecule on its own. A radical is often known as an <a href="/wiki/R_group_(disambiguation)" class="mw-redirect mw-disambig" title="R group (disambiguation)">R group</a>. The qualifier "free" was then needed to specify the unbound case. Following recent nomenclature revisions, a part of a larger molecule is now called a <a href="/wiki/Functional_group" title="Functional group">functional group</a> or <a href="/wiki/Substituent" title="Substituent">substituent</a>, and "radical" now implies "free". However, the old nomenclature may still appear in some books. </p><p>The term radical was already in use when the now obsolete <a href="/wiki/Radical_theory" title="Radical theory">radical theory</a> was developed. <a href="/wiki/Louis-Bernard_Guyton_de_Morveau" title="Louis-Bernard Guyton de Morveau">Louis-Bernard Guyton de Morveau</a> introduced the phrase "radical" in 1785 and the phrase was employed by <a href="/wiki/Antoine_Lavoisier" title="Antoine Lavoisier">Antoine Lavoisier</a> in 1789 in his <a href="/wiki/Trait%C3%A9_%C3%89l%C3%A9mentaire_de_Chimie" title="Traité Élémentaire de Chimie">Traité Élémentaire de Chimie</a>. A radical was then identified as the root base of certain acids (the Latin word "radix" meaning "root"). Historically, the term <i>radical</i> in <a href="/wiki/Radical_theory" title="Radical theory">radical theory</a> was also used for bound parts of the molecule, especially when they remain unchanged in reactions. These are now called <a href="/wiki/Functional_group" title="Functional group">functional groups</a>. For example, <a href="/wiki/Methanol" title="Methanol">methyl alcohol</a> was described as consisting of a methyl "radical" and a hydroxyl "radical". Neither are radicals in the modern chemical sense, as they are permanently bound to each other, and have no unpaired, reactive electrons; however, they can be observed as radicals in <a href="/wiki/Mass_spectrometry" title="Mass spectrometry">mass spectrometry</a> when broken apart by irradiation with energetic electrons. </p><p>In a modern context the first <a href="/wiki/Organic_compound" title="Organic compound">organic</a> (carbon–containing) radical identified was the <a href="/wiki/Triphenylmethyl_radical" title="Triphenylmethyl radical">triphenylmethyl radical</a>, (C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>C<sup>•</sup>. This species was discovered by <a href="/wiki/Moses_Gomberg" title="Moses Gomberg">Moses Gomberg</a> in 1900. In 1933 <a href="/wiki/Morris_S._Kharasch" title="Morris S. Kharasch">Morris S. Kharasch</a> and <a href="/wiki/Frank_R._Mayo" title="Frank R. Mayo">Frank Mayo</a> proposed that free radicals were responsible for <a href="/wiki/Anti-Markovnikov_addition" class="mw-redirect" title="Anti-Markovnikov addition">anti-Markovnikov addition</a> of <a href="/wiki/Hydrogen_bromide" title="Hydrogen bromide">hydrogen bromide</a> to <a href="/wiki/Allyl_bromide" title="Allyl bromide">allyl bromide</a>.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p><p>In most fields of chemistry, the historical definition of radicals contends that the molecules have nonzero electron spin. However, in fields including <a href="/wiki/Spectroscopy" title="Spectroscopy">spectroscopy</a> and <a href="/wiki/Astrochemistry" title="Astrochemistry">astrochemistry</a>, the definition is slightly different. <a href="/wiki/Gerhard_Herzberg" title="Gerhard Herzberg">Gerhard Herzberg</a>, who won the Nobel prize for his research into the electron structure and geometry of radicals, suggested a looser definition of free radicals: "any transient (chemically unstable) species (atom, molecule, or ion)".<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> The main point of his suggestion is that there are many chemically unstable molecules that have zero spin, such as C<sub>2</sub>, C<sub>3</sub>, CH<sub>2</sub> and so on. This definition is more convenient for discussions of transient chemical processes and astrochemistry; therefore researchers in these fields prefer to use this loose definition.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> </p> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(8)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="See_also">See also</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=25" title="Edit section: See also" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-8 collapsible-block" id="mf-section-8"> <ul><li><a href="/wiki/Electron_pair" title="Electron pair">Electron pair</a></li> <li><a href="/wiki/Globally_Harmonized_System_of_Classification_and_Labelling_of_Chemicals" title="Globally Harmonized System of Classification and Labelling of Chemicals">Globally Harmonized System of Classification and Labelling of Chemicals</a></li> <li><a href="/wiki/Hofmann%E2%80%93L%C3%B6ffler_reaction" title="Hofmann–Löffler reaction">Hofmann–Löffler reaction</a></li></ul> <dl><dt>Free radical research</dt></dl> <ul><li><a href="/wiki/Free_Radical_Centre" title="Free Radical Centre">ARC Centre of Excellence for Free Radical Chemistry and Biotechnology</a></li></ul> </section><div class="mw-heading mw-heading2 section-heading" onclick="mfTempOpenSection(9)"><span class="indicator mf-icon mf-icon-expand mf-icon--small"></span><h2 id="References">References</h2><span class="mw-editsection"> <a role="button" href="/w/index.php?title=Radical_(chemistry)&action=edit&section=26" title="Edit section: References" class="cdx-button cdx-button--size-large cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--icon-only cdx-button--weight-quiet "> <span class="minerva-icon minerva-icon--edit"></span> <span>edit</span> </a> </span> </div><section class="mf-section-9 collapsible-block" id="mf-section-9"> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">IUPAC Gold Book <a rel="nofollow" class="external text" href="http://goldbook.iupac.org/R05066.html"><i>radical (free radical)</i></a> <a rel="nofollow" class="external text" href="http://www.iupac.org/goldbook/R05066.pdf">PDF</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170302220258/http://goldbook.iupac.org/R05066.html">Archived</a> 2017-03-02 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon 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.citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFHayyanHashimAnjkut2016" class="citation journal cs1">Hayyan, M.; Hashim, M.A.; Anjkut, I.M. (2016). <a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Facs.chemrev.5b00407">"Superoxide Ion: Generation and Chemical Implications"</a>. <i>Chem. Rev</i>. <b>116</b> (5): 3029–85. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Facs.chemrev.5b00407">10.1021/acs.chemrev.5b00407</a></span>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/26875845">26875845</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Chem.+Rev.&rft.atitle=Superoxide+Ion%3A+Generation+and+Chemical+Implications&rft.volume=116&rft.issue=5&rft.pages=3029-85&rft.date=2016&rft_id=info%3Adoi%2F10.1021%2Facs.chemrev.5b00407&rft_id=info%3Apmid%2F26875845&rft.aulast=Hayyan&rft.aufirst=M.&rft.au=Hashim%2C+M.A.&rft.au=Anjkut%2C+I.M.&rft_id=https%3A%2F%2Fdoi.org%2F10.1021%252Facs.chemrev.5b00407&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-:1-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-:1_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:1_3-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-:1_3-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-:1_3-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFClayden,_JonathanGreevesWarren2012" class="citation book cs1">Clayden, Jonathan; Greeves, Nick; Warren, Stuart G. (2012). <a rel="nofollow" class="external text" href="https://www.worldcat.org/oclc/761379371"><i>Organic chemistry</i></a> (2nd ed.). Oxford: Oxford University Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-19-927029-3" title="Special:BookSources/978-0-19-927029-3"><bdi>978-0-19-927029-3</bdi></a>. <a href="/wiki/OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/761379371">761379371</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Organic+chemistry&rft.place=Oxford&rft.edition=2nd&rft.pub=Oxford+University+Press&rft.date=2012&rft_id=info%3Aoclcnum%2F761379371&rft.isbn=978-0-19-927029-3&rft.au=Clayden%2C+Jonathan&rft.au=Greeves%2C+Nick&rft.au=Warren%2C+Stuart+G.&rft_id=https%3A%2F%2Fwww.worldcat.org%2Foclc%2F761379371&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://polymerdatabase.com/polymer%20chemistry/Diaroyl%20Peroxides.html">"Diacyl Peroxides"</a>. <i>polymerdatabase.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2020-12-08</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=polymerdatabase.com&rft.atitle=Diacyl+Peroxides&rft_id=https%3A%2F%2Fpolymerdatabase.com%2Fpolymer%2520chemistry%2FDiaroyl%2520Peroxides.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGridnevIttel2001" class="citation journal cs1">Gridnev, Alexei A.; Ittel, Steven D. (2001). "Catalytic Chain Transfer in Free-Radical Polymerizations". <i>Chemical Reviews</i>. <b>101</b> (12): 3611–3660. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fcr9901236">10.1021/cr9901236</a>. <a href="/wiki/PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/11740917">11740917</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Chemical+Reviews&rft.atitle=Catalytic+Chain+Transfer+in+Free-Radical+Polymerizations&rft.volume=101&rft.issue=12&rft.pages=3611-3660&rft.date=2001&rft_id=info%3Adoi%2F10.1021%2Fcr9901236&rft_id=info%3Apmid%2F11740917&rft.aulast=Gridnev&rft.aufirst=Alexei+A.&rft.au=Ittel%2C+Steven+D.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMonroeWeed1993" class="citation journal cs1">Monroe, Bruce M.; Weed, Gregory C. (1993). "Photoinitiators for free-radical-initiated photoimaging systems". <i>Chemical Reviews</i>. <b>93</b>: 435–448. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fcr00017a019">10.1021/cr00017a019</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Chemical+Reviews&rft.atitle=Photoinitiators+for+free-radical-initiated+photoimaging+systems&rft.volume=93&rft.pages=435-448&rft.date=1993&rft_id=info%3Adoi%2F10.1021%2Fcr00017a019&rft.aulast=Monroe&rft.aufirst=Bruce+M.&rft.au=Weed%2C+Gregory+C.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSu2013" class="citation cs2">Su, Wei-Fang (2013), Su, Wei-Fang (ed.), "Radical Chain Polymerization", <i>Principles of Polymer Design and Synthesis</i>, Lecture Notes in Chemistry, vol. 82, Berlin, Heidelberg: Springer, pp. 137–183, <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-642-38730-2_7">10.1007/978-3-642-38730-2_7</a></span>, <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-3-642-38730-2" title="Special:BookSources/978-3-642-38730-2"><bdi>978-3-642-38730-2</bdi></a></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Principles+of+Polymer+Design+and+Synthesis&rft.atitle=Radical+Chain+Polymerization&rft.volume=82&rft.pages=137-183&rft.date=2013&rft_id=info%3Adoi%2F10.1007%2F978-3-642-38730-2_7&rft.isbn=978-3-642-38730-2&rft.aulast=Su&rft.aufirst=Wei-Fang&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-:2-8"><span class="mw-cite-backlink">^ <a href="#cite_ref-:2_8-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:2_8-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGrillerIngold1976" class="citation journal cs1">Griller, David; Ingold, Keith U. (1976). 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(1968). <i>Organic Chemistry of Stable Free Radicals</i>. London: Academic Press. pp. 1–6.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Organic+Chemistry+of+Stable+Free+Radicals&rft.pages=1-6&rft.pub=London%3A+Academic+Press&rft.date=1968&rft.aulast=Forrester&rft.aufirst=A.R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFOakley1988" class="citation book cs1">Oakley, Richard T. (1988). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20150923202507/http://www.chembio.uoguelph.ca/oakley/papers/rto_086.pdf">"Cyclic and Heterocyclic Thiazenes"</a> <span class="cs1-format">(PDF)</span>. <i>Progress in Inorganic Chemistry</i>. Cyclic and Heterocyclic Thiazenes (section). Vol. 36. pp. 299–391. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F9780470166376.ch4">10.1002/9780470166376.ch4</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-470-16637-6" title="Special:BookSources/978-0-470-16637-6"><bdi>978-0-470-16637-6</bdi></a>. Archived from <a rel="nofollow" class="external text" href="http://www.chembio.uoguelph.ca/oakley/papers/rto_086.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2015-09-23<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-31</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Cyclic+and+Heterocyclic+Thiazenes&rft.btitle=Progress+in+Inorganic+Chemistry&rft.pages=299-391&rft.date=1988&rft_id=info%3Adoi%2F10.1002%2F9780470166376.ch4&rft.isbn=978-0-470-16637-6&rft.aulast=Oakley&rft.aufirst=Richard+T.&rft_id=http%3A%2F%2Fwww.chembio.uoguelph.ca%2Foakley%2Fpapers%2Frto_086.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3ARadical+%28chemistry%29" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRawsonBanisterLavender1995" class="citation book cs1">Rawson, J; Banister, A; Lavender, I (1995). <i>The Chemistry of Dithiadiazolylium and Dithiadiazolyl Rings**Dedicated to Dr. Z. V. 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title="جذر كيميائي – Arabic" lang="ar" hreflang="ar" data-title="جذر كيميائي" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Radikal_(kimya)" title="Radikal (kimya) – Azerbaijani" lang="az" hreflang="az" data-title="Radikal (kimya)" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%AE%E0%A7%82%E0%A6%B2%E0%A6%95" title="মূলক – Bangla" lang="bn" hreflang="bn" data-title="মূলক" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%A1%D0%B2%D0%B0%D0%B1%D0%BE%D0%B4%D0%BD%D1%8B%D1%8F_%D1%80%D0%B0%D0%B4%D1%8B%D0%BA%D0%B0%D0%BB%D1%8B" title="Свабодныя радыкалы – Belarusian" lang="be" hreflang="be" data-title="Свабодныя радыкалы" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D0%B8%D0%BC%D0%B8%D1%8F)" title="Радикал (химия) – Bulgarian" lang="bg" hreflang="bg" data-title="Радикал (химия)" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Radikal_(hemija)" title="Radikal (hemija) – Bosnian" lang="bs" hreflang="bs" data-title="Radikal (hemija)" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Radical_qu%C3%ADmic" title="Radical químic – Catalan" lang="ca" hreflang="ca" data-title="Radical químic" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cv mw-list-item"><a href="https://cv.wikipedia.org/wiki/%D0%98%D1%80%C4%95%D0%BA%D0%BB%C4%95_%D1%80%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB%D1%81%D0%B5%D0%BC" title="Ирĕклĕ радикалсем – Chuvash" lang="cv" hreflang="cv" data-title="Ирĕклĕ радикалсем" data-language-autonym="Чӑвашла" data-language-local-name="Chuvash" class="interlanguage-link-target"><span>Чӑвашла</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Radik%C3%A1l" title="Radikál – Czech" lang="cs" hreflang="cs" data-title="Radikál" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Radikal_(kemi)" title="Radikal (kemi) – Danish" lang="da" hreflang="da" data-title="Radikal (kemi)" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Radikal_(Chemie)" title="Radikal (Chemie) – German" lang="de" hreflang="de" data-title="Radikal (Chemie)" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Radikaal" title="Radikaal – Estonian" lang="et" hreflang="et" data-title="Radikaal" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%A7%CE%B7%CE%BC%CE%B9%CE%BA%CE%AE_%CF%81%CE%AF%CE%B6%CE%B1" title="Χημική ρίζα – Greek" lang="el" hreflang="el" data-title="Χημική ρίζα" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Radical_(qu%C3%ADmica)" title="Radical (química) – Spanish" lang="es" hreflang="es" data-title="Radical (química)" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Radikalo_(%C4%A5emio)" title="Radikalo (ĥemio) – Esperanto" lang="eo" hreflang="eo" data-title="Radikalo (ĥemio)" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Erradikal_aske" title="Erradikal aske – Basque" lang="eu" hreflang="eu" data-title="Erradikal aske" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%B1%D8%A7%D8%AF%DB%8C%DA%A9%D8%A7%D9%84_%D8%A2%D8%B2%D8%A7%D8%AF" title="رادیکال آزاد – Persian" lang="fa" hreflang="fa" data-title="رادیکال آزاد" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Radical_(chimie)" title="Radical (chimie) – French" lang="fr" hreflang="fr" data-title="Radical (chimie)" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/Fr%C3%A9amh_(ceimic)" title="Fréamh (ceimic) – Irish" lang="ga" hreflang="ga" data-title="Fréamh (ceimic)" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Radical_(qu%C3%ADmica)" title="Radical (química) – Galician" lang="gl" hreflang="gl" data-title="Radical (química)" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%9C%A0%EB%A6%AC%EA%B8%B0" title="유리기 – Korean" lang="ko" hreflang="ko" data-title="유리기" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D4%B1%D5%A6%D5%A1%D5%BF_%D5%BC%D5%A1%D5%A4%D5%AB%D5%AF%D5%A1%D5%AC%D5%B6%D5%A5%D6%80" title="Ազատ ռադիկալներ – Armenian" lang="hy" hreflang="hy" data-title="Ազատ ռադիկալներ" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%AE%E0%A5%82%E0%A4%B2%E0%A4%95" title="मूलक – Hindi" lang="hi" hreflang="hi" data-title="मूलक" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Radikal_(kemija)" title="Radikal (kemija) – Croatian" lang="hr" hreflang="hr" data-title="Radikal (kemija)" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Radikal_bebas" title="Radikal bebas – Indonesian" lang="id" hreflang="id" data-title="Radikal bebas" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-os mw-list-item"><a href="https://os.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D0%B8%D0%BC%D0%B8)" title="Радикал (хими) – Ossetic" lang="os" hreflang="os" data-title="Радикал (хими)" data-language-autonym="Ирон" data-language-local-name="Ossetic" class="interlanguage-link-target"><span>Ирон</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/Sindurefni" title="Sindurefni – Icelandic" lang="is" hreflang="is" data-title="Sindurefni" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Radicale_libero" title="Radicale libero – Italian" lang="it" hreflang="it" data-title="Radicale libero" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%A8%D7%93%D7%99%D7%A7%D7%9C%D7%99%D7%9D_%D7%97%D7%95%D7%A4%D7%A9%D7%99%D7%99%D7%9D" title="רדיקלים חופשיים – Hebrew" lang="he" hreflang="he" data-title="רדיקלים חופשיים" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%97%E1%83%90%E1%83%95%E1%83%98%E1%83%A1%E1%83%A3%E1%83%A4%E1%83%90%E1%83%9A%E1%83%98_%E1%83%A0%E1%83%90%E1%83%93%E1%83%98%E1%83%99%E1%83%90%E1%83%9A%E1%83%94%E1%83%91%E1%83%98" title="თავისუფალი რადიკალები – Georgian" lang="ka" hreflang="ka" data-title="თავისუფალი რადიკალები" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Br%C4%ABvais_radik%C4%81lis" title="Brīvais radikālis – Latvian" lang="lv" hreflang="lv" data-title="Brīvais radikālis" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Radikalas_(chemija)" title="Radikalas (chemija) – Lithuanian" lang="lt" hreflang="lt" data-title="Radikalas (chemija)" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Gy%C3%B6k_(k%C3%A9mia)" title="Gyök (kémia) – Hungarian" lang="hu" hreflang="hu" data-title="Gyök (kémia)" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D0%B5%D0%BC%D0%B8%D1%98%D0%B0)" title="Радикал (хемија) – Macedonian" lang="mk" hreflang="mk" data-title="Радикал (хемија)" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Radikal_bebas" title="Radikal bebas – Malay" lang="ms" hreflang="ms" data-title="Radikal bebas" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D0%B8%D0%BC%D0%B8)" title="Радикал (хими) – Mongolian" lang="mn" hreflang="mn" data-title="Радикал (хими)" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Radicaal_(scheikunde)" title="Radicaal (scheikunde) – Dutch" lang="nl" hreflang="nl" data-title="Radicaal (scheikunde)" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ne mw-list-item"><a href="https://ne.wikipedia.org/wiki/%E0%A4%B0%E0%A5%87%E0%A4%A1%E0%A4%BF%E0%A4%95%E0%A4%B2" title="रेडिकल – Nepali" lang="ne" hreflang="ne" data-title="रेडिकल" data-language-autonym="नेपाली" data-language-local-name="Nepali" class="interlanguage-link-target"><span>नेपाली</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%83%A9%E3%82%B8%E3%82%AB%E3%83%AB_(%E5%8C%96%E5%AD%A6)" title="ラジカル (化学) – Japanese" lang="ja" hreflang="ja" data-title="ラジカル (化学)" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Frie_radikaler" title="Frie radikaler – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Frie radikaler" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Fritt_radikal" title="Fritt radikal – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Fritt radikal" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Kimyoviy_radikallar" title="Kimyoviy radikallar – Uzbek" lang="uz" hreflang="uz" data-title="Kimyoviy radikallar" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Rodniki" title="Rodniki – Polish" lang="pl" hreflang="pl" data-title="Rodniki" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Radical_(qu%C3%ADmica)" title="Radical (química) – Portuguese" lang="pt" hreflang="pt" data-title="Radical (química)" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Radical_(chimie)" title="Radical (chimie) – Romanian" lang="ro" hreflang="ro" data-title="Radical (chimie)" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-rue mw-list-item"><a href="https://rue.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D0%B5%D0%BC%D0%B8%D1%8F)" title="Радикал (хемия) – Rusyn" lang="rue" hreflang="rue" data-title="Радикал (хемия)" data-language-autonym="Русиньскый" data-language-local-name="Rusyn" class="interlanguage-link-target"><span>Русиньскый</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%A1%D0%B2%D0%BE%D0%B1%D0%BE%D0%B4%D0%BD%D1%8B%D0%B5_%D1%80%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB%D1%8B" title="Свободные радикалы – Russian" lang="ru" hreflang="ru" data-title="Свободные радикалы" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sco mw-list-item"><a href="https://sco.wikipedia.org/wiki/Radical_(chemistry)" title="Radical (chemistry) – Scots" lang="sco" hreflang="sco" data-title="Radical (chemistry)" data-language-autonym="Scots" data-language-local-name="Scots" class="interlanguage-link-target"><span>Scots</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/Radikali_(kimi)" title="Radikali (kimi) – Albanian" lang="sq" hreflang="sq" data-title="Radikali (kimi)" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Free_radical" title="Free radical – Simple English" lang="en-simple" hreflang="en-simple" data-title="Free radical" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Radik%C3%A1l_(ch%C3%A9mia)" title="Radikál (chémia) – Slovak" lang="sk" hreflang="sk" data-title="Radikál (chémia)" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Radikal_(kemija)" title="Radikal (kemija) – Slovenian" lang="sl" hreflang="sl" data-title="Radikal (kemija)" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/Radikal_(hemija)" title="Radikal (hemija) – Serbian" lang="sr" hreflang="sr" data-title="Radikal (hemija)" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Radikal_(hemija)" title="Radikal (hemija) – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Radikal (hemija)" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-su mw-list-item"><a href="https://su.wikipedia.org/wiki/Radikal_(kimia)" title="Radikal (kimia) – Sundanese" lang="su" hreflang="su" data-title="Radikal (kimia)" data-language-autonym="Sunda" data-language-local-name="Sundanese" class="interlanguage-link-target"><span>Sunda</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Radikaali_(kemia)" title="Radikaali (kemia) – Finnish" lang="fi" hreflang="fi" data-title="Radikaali (kemia)" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Fri_radikal" title="Fri radikal – Swedish" lang="sv" hreflang="sv" data-title="Fri radikal" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AE%E0%AF%82%E0%AE%B2%E0%AE%BF%E0%AE%95%E0%AE%AE%E0%AF%8D" title="மூலிகம் – Tamil" lang="ta" hreflang="ta" data-title="மூலிகம்" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-tt mw-list-item"><a href="https://tt.wikipedia.org/wiki/%C4%B0rekle_radikallar" title="İrekle radikallar – Tatar" lang="tt" hreflang="tt" data-title="İrekle radikallar" data-language-autonym="Татарча / tatarça" data-language-local-name="Tatar" class="interlanguage-link-target"><span>Татарча / tatarça</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B8%AD%E0%B8%99%E0%B8%B8%E0%B8%A1%E0%B8%B9%E0%B8%A5%E0%B8%AD%E0%B8%B4%E0%B8%AA%E0%B8%A3%E0%B8%B0" title="อนุมูลอิสระ – Thai" lang="th" hreflang="th" data-title="อนุมูลอิสระ" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Radikal_(kimya)" title="Radikal (kimya) – Turkish" lang="tr" hreflang="tr" data-title="Radikal (kimya)" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A0%D0%B0%D0%B4%D0%B8%D0%BA%D0%B0%D0%BB_(%D1%85%D1%96%D0%BC%D1%96%D1%8F)" title="Радикал (хімія) – Ukrainian" lang="uk" hreflang="uk" data-title="Радикал (хімія)" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/G%E1%BB%91c_t%E1%BB%B1_do" title="Gốc tự do – Vietnamese" lang="vi" hreflang="vi" data-title="Gốc tự do" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/%E8%87%AA%E7%94%B1%E5%9F%BA" title="自由基 – Wu" lang="wuu" hreflang="wuu" data-title="自由基" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E6%B8%B8%E9%9B%A2%E5%9F%BA" title="游離基 – Cantonese" lang="yue" hreflang="yue" data-title="游離基" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target"><span>粵語</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E8%87%AA%E7%94%B1%E5%9F%BA" title="自由基 – Chinese" lang="zh" hreflang="zh" data-title="自由基" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li></ul> </section> </div> <div class="minerva-footer-logo"><img src="/static/images/mobile/copyright/wikipedia-wordmark-en.svg" alt="Wikipedia" width="120" height="18" style="width: 7.5em; height: 1.125em;"/> </div> <ul id="footer-info" class="footer-info hlist hlist-separated"> <li id="footer-info-lastmod"> This page was last edited on 27 November 2024, at 23:02<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Content is available under <a class="external" rel="nofollow" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">CC 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