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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head profile="http://gmpg.org/xfn/1"> <title>Computational Organic Chemistry » cyclobutadiene</title> <meta name="google-site-verification" content="g1Myv4tUVAmqRbwZeBi7IPuSZpP64RWjVJ6itIoouCo"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <style type="text/css" media="screen">@import url( /blog/wp-content/themes/comporg/style.css);</style> <link rel="stylesheet" id="wp-block-library-css" href="/blog/wp-includes/css/dist/block-library/style.min.css?ver=5.6.1" type="text/css" media="all"> <script type="text/javascript">  </script> </head> <body> <div id="header"> <div id="header_img"></div> </div> <div id="link_section"> <div style="float:left"> <a href="/blog/about">About this Blog</a> | <a href="/">Book Homepage</a> | <a href="http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471713422.html">Purchase the Book</a> </div> </div> <div id="after_links"></div> <div id="content"> <div id="main"> <h2 class="post-title">Archive for the 'cyclobutadiene' Category</h2> <div class="box"> <h2><a href="/blog/archives/4059" rel="bookmark" title="Permanent Link: Triplet cyclobutadiene">Triplet cyclobutadiene</a></h2> <div class="post-content"> <p>Cyclobutadiene has long fascinated organic chemists. It is the 4e analogue of the 6e benzene molecule, yet it could hardly be more different. Despite nearly a century of effort, cyclobutadiene analogues were only first prepared in the 1970s, reflecting its strong antiaromatic character.</p> <p>Per-trimethylsilylcyclobutadiene <b>1</b> offers opportunities to probe the properties of the cyclobutadiene ring as the bulky substituents diminish dimerization and polymerization of the reactive π-bonds. Kostenko and coworkers have now reported on the triplet state of <b>1</b>.<a href="#cybutTrip"><sup>1</sup></a> They observe three EPR signals of <b>1</b> at temperatures above 350 K, and these signals increase in area with increasing temperature. This is strong evidence for the existence of triplet <b>1</b> in equilibrium with the lower energy singlet. Using the variable temperature EPR spectra, the singlet triplet gap is 13.9 ± 0.8 kcal mol<sup>-1</sup>.</p> <p align="center"><img src="/blog/wp-content/cybutTMSimg.png"></p> <p>The structures of singlet and triplet <b>1</b> were optimized at B3LYP-D3/6-311+G(d,p) and shown in Figure 1. The singlet is the expected rectangle, with distinctly different C-C distance around the ring. The triplet is a square, with equivalent C-C distances. Since both the singlet and triplet states are likely to have multireference character, the energies of both states were obtained at RI-MRDDCI2-CASSCF(4,4)/def2-SVP//B3LYPD3/6-311+G(d,p) and give a singlet-triplet gap of 11.8 kcal mol<sup>-1</sup>, in quite reasonable agreement with experiment.</p> <table align="center" border="0" cellspacing="0" cellpadding="4"> <tr align="center" valign="bottom"> <td> <p></p> <div class="jmol" id="cybutTMSs"> <a onclick="return false"><br> <img src="/blog/wp-content/cybutTMSs.png" onclick="insertJmol('cybutTMSs',300,300,'cybutTMSs.xyz')"></a> </div> <p>singlet</p> </td> <td> <p></p> <div class="jmol" id="cybutTMSt"> <a onclick="return false"><br> <img src="/blog/wp-content/cybutTMSt.png" onclick="insertJmol('cybutTMSt',300,300,'cybutTMSt.xyz')"></a> </div> <p>triplet</p> </td> </tr> </table> <p align="center"><b>Figure 1</b>. Optimized geometries of singlet and triplet <b>1</b>.</p> <h3>References</h3> <p><a name="cybutTrip"></a></p> <p>1. Kostenko, A.; Tumanskii, B.; Kobayashi, Y.; Nakamoto, M.; Sekiguchi, A.; Apeloig, Y., "Spectroscopic Observation of the Triplet Diradical State of a Cyclobutadiene." <i>Angew. Chem. Int. Ed.</i> <b>2017</b>, <i>56</i>, 10183-10187, DOI: <a href="http://dx.doi.org/10.1002/anie.201705228">10.1002/anie.201705228</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1S/C16H36Si4/c1-17(2,3)13-14(18(4,5)6)16(20(10,11)12)15(13)19(7,8)9/h1-12H3<br>InChIkey=AYOHYRSQVCLGKR-UHFFFAOYSA-N</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/aromaticity" rel="category tag">Aromaticity</a> &<a href="/blog/archives/category/molecules/cyclobutadiene" rel="category tag">cyclobutadiene</a></span> <span class="user">Steven Bachrach</span> <span class="date">11 Sep 2017</span> <span class="comments"><a href="/blog/archives/4059#comments">1 Comment</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/2102" rel="bookmark" title="Permanent Link: Ethynyl-substituted Cyclobutadiene">Ethynyl-substituted Cyclobutadiene</a></h2> <div class="post-content"> <p>Cyclobutadiene is the prototypical antiaromatic compound. McMahon has examined the<br> effect of ethynyl substitution on this ring, with a long term eye towards the possibility of these types of species being involved in the synthesis of fullerenes.<a ref="#ethynCB"><sup>1</sup></a></p> <p>All of the possible ethynyl-substituted cyclobutadiene species (<b>1-7</b>) were optimized at B3LYP/6-31G(d) and CCSD/cc-pVDZ in their singlet and triplet states.</p> <p align="center"><img src="/blog/wp-content/ethynylCBfig.gif"></p> <p>The structures of singlet and triplet <b>7</b> are shown in Figure 1. The geometries provided by the two different methods are quite similar. They show a rectangular form for the singlets and a delocalized, nearly square ring for the triplets.</p> <table align="center" border="0" cellspacing="0" cellpadding="3"> <tr align="center"> <td> <p></p> <div class="jmol" id="4ethCBS"> <a onclick="return false"><br> <img src="/blog/wp-content/4ethynylCBS.jpg" onclick="insertJmol('4ethCBS',300,300,'4ethynylCBS.xyz')"><br> </a> </div> <p><b>7<sub>singlet</sub></b></p> </td> <td> <p></p> <div class="jmol" id="4ethCBT"> <a onclick="return false"><br> <img src="/blog/wp-content/4ethynylCBT.jpg" onclick="insertJmol('4ethCBT',300,300,'4ethynylCBT.xyz')"><br> </a> </div> <p><b>7<sub>triplet</sub></b></p> </td> </tr> </table> <p align="center"><b>Figure 1.</b> CCSD/cc-pVDZ optimized structures of singlet and triplet <b>7</b>.</p> <p>The computed singlet-triplet gap decreases with each ethynyl substituent. B3LYP, which overestimates the stability of triplets, predicts that <b>6</b> and <b>7</b> will be ground state triplets, while CCSD predicts a singlet ground state for all 7 species, with the gap decreasing steadily from 11.5 to 8.2 kcal mol<sup>-1</sup>, a value that is also probably underestimated.</p> <p>This change in the singlet-triplet gap reflects a stronger stabilizing effect of each ethynyl group to the cycnobutadiene ring for the triplet than for the singlet state. This is seen in the homodesmotic stabilization energies.</p> <p>Lastly, NICS(1)<sub>zz</sub> values are positive for all of the singlets and negative for the triplets. The positive values for the singlets reflect their antiaromatic character, also seen in the alternant bond distances around the ring. The NICS values of the singlets decrease with increasing substitution. The negative NICS values of the triplets reflects aromatic character, as seen in the non-alternant distances around the ring. Interestingly, the triplet NICS values decrease with increasing ethynyl substitution, suggesting decreased aromaticity, even though the homodesmotic reactions suggest increasing stabilization with substitution.</p> <h3>References</h3> <p><a name="ethynCB"></a></p> <p>(1) Esselman, B. J.; McMahon, R. J., "Effects of Ethynyl Substitution on Cyclobutadiene," <i>J. Phys. Chem. A</i> <b>2012</b>, <i>116</i>, 483-490, DOI: <a href="http://dx.doi.org/10.1021/jp206478q">10.1021/jp206478q</a></p> <h3>InChIs</h3> <p><b>1</b>: InChI=1/C4H4/c1-2-4-3-1/h1-4H<br>InChIKey=HWEQKSVYKBUIIK-UHFFFAOYAI</p> <p><b>2</b>: InChI=1/C6H4/c1-2-6-4-3-5-6/h1,3-5H<br>InChIKey=XFHXCHFBSJDBGT-UHFFFAOYAG</p> <p><b>3</b>: InChI=1/C8H4/c1-3-7-5-6-8(7)4-2/h1-2,5-6H<br>InChIKey=YSSBCMLQKUIAEP-UHFFFAOYAI</p> <p><b>4</b>: InChI=1/C8H4/c1-3-7-5-8(4-2)6-7/h1-2,5-6H<br>InChIKey=IRAQOGPKMAXTQY-UHFFFAOYAN</p> <p><b>5</b>: InChI=1/C8H4/c1-3-7-5-6-8(7)4-2/h1-2,5-6H<br>InChIKey=YSSBCMLQKUIAEP-UHFFFAOYAI</p> <p><b>6</b>: InChI=1/C10H4/c1-4-8-7-9(5-2)10(8)6-3/h1-3,7H<br>InChIKey=BVCIPPXDFXWTJR-UHFFFAOYAQ</p> <p><b>7</b>: InChI=1/C12H4/c1-5-9-10(6-2)12(8-4)11(9)7-3/h1-4H<br>InChIKey=HEUYILYXFVQGOW-UHFFFAOYAO</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/molecules/cyclobutadiene" rel="category tag">cyclobutadiene</a></span> <span class="user">Steven Bachrach</span> <span class="date">20 Mar 2012</span> <span class="comments"><a href="/blog/archives/2102#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/1394" rel="bookmark" title="Permanent Link: Has a cyclobutadiene species been isolated? (Part 2)">Has a cyclobutadiene species been isolated? (Part 2)</a></h2> <div class="post-content"> <p>Henry Rzepa’s response<a href="#RzepaCB1"><sup>1</sup></a> to the reported detection and x-ray structure of 1,3-dimethylcyclobutadiene<a href="#RzepaCB2"><sup>2</sup></a> has now been published. He takes a different tack than those take by Alabugin<a href="#RzepaCB3"><sup>3</sup></a> and Scheschkewitz<a href="#RzepaCB4"><sup>4</sup></a> in refuting the analysis of this work (see this earlier <a href="/blog/archives/1324">post</a>). Rzepa discuses computations to evaluate the possible lifetime of 1,3-dimethylcyclobutadiene in the vicinity of CO<sub>2</sub>. In particular, he examines the barrier for the allowed [4+2] cycloaddition to give back the lactone <b>1</b> (Reaction 1), which was photolyzed in the experiment to produce the cyclobutadiene and CO<sub>2</sub> species in the first place.</p> <table border="0" cellspacing="0" cellpadding="3" align="center"> <tr align="center" valign="middle"> <td> <p><img src="/blog/wp-content/rzepaCB1.gif"></p> </td> <td> <p>Reaction 1</p> </td> </tr> </table> <p>The gas phase free energy barrier at 175 K (the experimental condition) computed at ωB97XD/6-311G(d,p) is 16.8 kcal mol<sup>-1</sup>, which is sufficiently high to limit this back reaction. Embedding this into a water continuum lowers the barrier to 12.9 kcal mol<sup>-1</sup>.</p> <p>But the experiment has these species embedded inside a calixarene host along with guanidinum<br> cations. The cation could associate with the CO<sub>2</sub> (indicated in Reaction 1 as X), and inclusion of a guanidinium in the gas phase, reduces the barrier to 3.3 kcal mol<sup>-1</sup>. Rerunning this computation now with a water continuum produce an intermediate zwitterion formed by making the C-C bond, and the second step makes the C-O bond.</p> <p>Finally, modeling the reaction with guanidium inside a calixarene host leads to a barrier of 8 kcal<br> mol<sup>-1</sup>, 10.5 kcal mol<sup>-1</sup> with water continuum. Rzepa concludes that recombination of 1,3-dimethylcyclobutadiene and CO<sub>2</sub> to give <b>1</b> should be too fast on the timescale of the experiment for observation of the cyclobutadiene. This argument, along with the two previous papers, strongly casts doubt on the original claim.</p> <p>I should point out that Henry has deposited all the structures in a <a href="http://www.rsc.org/suppdata/CC/c0/c0cc04023a/Table1/index.html">nice enhanced table</a>. You may need a subscription to get to this – I have not checked the access conditions.</p> <h3>References</h3> <p><a name="RzepaCB1"></a></p> <p>(1) Rzepa, H. S., "Can 1,3-dimethylcyclobutadiene and carbon dioxide co-exist inside<br> a supramolecular cavity?," <i>Chem. Commun.</i> <b>2011</b>, ASAP, DOI: <a href="http://dx.doi.org/10.1039/C0CC04023A">10.1039/C0CC04023A</a></p> <p><a name="RzepaCB2"></a></p> <p>(2) Legrand, Y.-M.; van der Lee, A.; Barboiu, M., "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix," <i>Science</i> <b>2010</b>, <i>329</i>, 299-302, DOI: <a href="http://dx.doi.org/10.1126/science.1188002">10.1126/science.1188002</a>.</p> <p><a name="RzepaCB3"></a></p> <p> (3) Alabugin, I. V.; Gold, B.; Shatruk, M.; Kovnir, K., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," <i>Science</i>, <b>2010</b>, <i>330</i>, 1047, DOI: <a href="http://dx.doi.org/10.1126/science.1196188">10.1126/science.1196188</a>.</p> <p><a name="RzepaCB4"></a></p> <p>(4) Scheschkewitz, D., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," <i>Science</i>, <b>2010</b>, <i>330</i>, 1047, DOI: <a href="http://dx.doi.org/10.1126/science.1195752">10.1126/science.1195752</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1/C7H8O2/c1-4-3-7(2)5(4)6(8)9-7/h3,5H,1-2H3<br> InChIKey=GLYAMHMFKKLRAL-UHFFFAOYAT</p> <p><b>1,3-dimethylcyclobutadiene</b>: InChI=1/C6H8/c1-5-3-6(2)4-5/h3-4H,1-2H3<br> InChIKey=ADQGKIKNUMJFSL-UHFFFAOYAU</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/molecules/cyclobutadiene" rel="category tag">cyclobutadiene</a></span> <span class="user">Steven Bachrach</span> <span class="date">18 Jan 2011</span> <span class="comments"><a href="/blog/archives/1394#respond">No Comments</a></span> </p> </div> <div class="box"> <h2><a href="/blog/archives/1324" rel="bookmark" title="Permanent Link: Has a cyclobutadiene species been isolated?">Has a cyclobutadiene species been isolated?</a></h2> <div class="post-content"> <p>Earlier this year, Barboiu made the astonishing claim of the x-ray characterization of 1,3-dimethylcyclobutadiene, brought about by the photolysis of 4,6-dimethyl-α-pyrone encapsulated in a guanidinium-sulfonate-calixarene crystal (Reaction 1).<a href="#cbdR1"><sup>1</sup></a> I had not blogged on this paper because Henry Rzepa did a quite thorough analysis of it in this <a href="http://rzepa.net/blog/?p=2355">blog post</a>. Now, a couple of rebuttals have appeared and it is time to examine this study.</p> <p align="center"><img src="/blog/wp-content/cbdScheme1.gif"></p> <p>Alabugin calls in question whether the reaction has in fact proceeded beyond <b>2</b>.<a href="#cbdR2"><sup>2</sup></a> They note that in the x-ray crystal structure, the distance between a carbon of the purported cyclobutadiene ring and the carbon of CO<sub>2</sub> is only 1.50 and 1.61 Å. Barboiu called this a “strong van der Waals contact”, but this is a distance much more attributable to a covalent bond. In fact, the shorter distance is in fact shorter than some of the other C-C distances in the structure that Barboiu calls covalent! Perhaps more bizarre is that the putative CO<sub>2</sub> fragment is highly bent: 119.9&;deg;, a value inconsistent with CO<sub>2</sub> but perfectly ordinary for an sp<sup>2</sup> carbon. In fact, B3LYP/6-31G** computations suggest that bending CO<sub>2</sub> this much costs about 75 kcal mol<sup>-1</sup> – and tack on another 7 kcal mol<sup>-1</sup> to make the two C-O distances unequal (as found in the x-ray structure!). Thus, Alabugin suggests that only <b>2</b> has been formed, and notes that the cleavage to <b>3</b> would likely require light of much higher energy that that used in the Barboiu experiment.</p> <p>Scheschkewitz argues that the x-ray data can be better interpreted as suggesting only the Dewar β-lactone <b>2</b> is present, though in its two enantiomeric forms.<a href="#cbdR3"><sup>3</sup></a> There is no evidence, he suggests of any cyclobutadiene component at all.</p> <p>It should be noted that Barboiu stands<a href="#cbdR4"><sup>4</sup></a> by his original work and original assignment, claiming that these types of x-ray experiments are quite difficult and large error bars in atom positions are inherent to the study.</p> <p>Henry Rzepa has <a href="http://www.ch.ic.ac.uk/rzepa/blog/?p=2828">blogged again on this controversy</a> and has a paper coming out on this soon. I shall update when it appears. Henry notes in one of the comments to his blog that a TD-DFT computations does show that the Dewar β-lactone <b>2</b> is transparent from 320-500nm. </p> <h3>References</h3> <p><a name="cbdR1"></a></p> <p>(1) Legrand, Y.-M.; van der Lee, A.; Barboiu, M., "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix," <i>Science</i> <b>2010</b>, <i>329</i>, 299-302, DOI: <a href="http://dx.doi.org/10.1126/science.1188002">10.1126/science.1188002</a>.</p> <p><a name="cbdR2"></a></p> <p>(2) Alabugin, I. V.; Gold, B.; Shatruk, M.; Kovnir, K., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," <i>Science</i>, <i>330</i>, 1047, DOI: <a href="http://dx.doi.org/10.1126/science.1196188">10.1126/science.1196188</a>.</p> <p><a name="cbdR3"></a></p> <p>(3) Scheschkewitz, D., "Comment on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," <i>Science</i> <b>2010</b>, <i>330</i>, 1047, DOI: <a href="http://dx.doi.org/10.1126/science.1195752">10.1126/science.1195752</a>.</p> <p><a name="cbdR4"></a></p> <p>(4) Legrand, Y.-M.; van der Lee, A.; Barboiu, M., "Response to Comments on "Single-Crystal X-ray Structure of 1,3-Dimethylcyclobutadiene by Confinement in a Crystalline Matrix"," <i>Science</i>, <i>330</i>, 1047, DOI: <a href="http://dx.doi.org/10.1126/science.1195846">10.1126/science.1195846</a>.</p> <h3>InChIs</h3> <p><b>1</b>: InChI=1/C7H8O2/c1-5-3-6(2)9-7(8)4-5/h3-4H,1-2H3<br>InChIKey=IXYLIUKQQQXXON-UHFFFAOYA</p> <p><b>2</b>: InChI=1/C7H8O2/c1-4-3-7(2)5(4)6(8)9-7/h3,5H,1-2H3<br>InChIKey=GLYAMHMFKKLRAL-UHFFFAOYAT</p> <p><b>3</b>: InChI=1/C6H8/c1-5-3-6(2)4-5/h3-4H,1-2H3<br>InChIKey=ADQGKIKNUMJFSL-UHFFFAOYAU</p>  </div> <p class="bottom"> <span class="cat"><a href="/blog/archives/category/aromaticity" rel="category tag">Aromaticity</a> &<a href="/blog/archives/category/molecules/cyclobutadiene" rel="category tag">cyclobutadiene</a></span> <span class="user">Steven Bachrach</span> <span class="date">22 Nov 2010</span> <span class="comments"><a href="/blog/archives/1324#comments">5 Comments</a></span> </p> </div> <p align="center"></p> </div> <div id="sidebar"> <ul> <li class="box"> <h2> Categories </h2> <ul> <li class="cat-item cat-item-25"> <a href="/blog/archives/category/acidity">Acidity</a> (12) </li> <li class="cat-item cat-item-3"> <a href="/blog/archives/category/aromaticity">Aromaticity</a> (91) </li> 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href="/blog/archives/category/authors/schreiner">Schreiner</a> (29) </li> <li class="cat-item cat-item-6"> <a href="/blog/archives/category/authors/singleton">Singleton</a> (11) </li> <li class="cat-item cat-item-18"> <a href="/blog/archives/category/authors/truhlar">Truhlar</a> (8) </li> </ul> </li> <li class="cat-item cat-item-15"> <a href="/blog/archives/category/bond-dissociation-energy">Bond Dissociation Energy</a> (6) </li> <li class="cat-item cat-item-81"> <a href="/blog/archives/category/bsse">BSSE</a> (1) </li> <li class="cat-item cat-item-88"> <a href="/blog/archives/category/cyclophane">cyclophane</a> (0) </li> <li class="cat-item cat-item-4"> <a href="/blog/archives/category/dynamics">Dynamics</a> (35) </li> <li class="cat-item cat-item-57"> <a href="/blog/archives/category/e-publishing">E-publishing</a> (7) </li> <li class="cat-item cat-item-65"> <a href="/blog/archives/category/enzyme">Enzyme</a> (4) </li> <li class="cat-item cat-item-95"> <a href="/blog/archives/category/fep">FEP</a> (1) </li> <li class="cat-item cat-item-86"> <a href="/blog/archives/category/host-guest">host-guest</a> (6) </li> <li class="cat-item cat-item-84"> <a href="/blog/archives/category/hydrogen-bond">Hydrogen bond</a> (5) </li> <li class="cat-item cat-item-91"> <a href="/blog/archives/category/ion-pairs">Ion Pairs</a> (1) </li> <li class="cat-item cat-item-74"> <a href="/blog/archives/category/isotope-effects">Isotope Effects</a> (5) </li> <li class="cat-item cat-item-67"> <a href="/blog/archives/category/keto-enol-tautomerization">Keto-enol tautomerization</a> (3) </li> <li class="cat-item cat-item-54 current-cat-parent current-cat-ancestor"> <a href="/blog/archives/category/molecules">Molecules</a> (100) <ul class="children"> <li class="cat-item cat-item-48"> <a href="/blog/archives/category/molecules/adamantane">adamantane</a> (3) </li> <li class="cat-item cat-item-26"> <a href="/blog/archives/category/molecules/amino-acids">amino acids</a> (13) </li> <li class="cat-item cat-item-19"> <a href="/blog/archives/category/molecules/annulenes">annulenes</a> (8) </li> <li class="cat-item cat-item-27"> <a href="/blog/archives/category/molecules/benzynes">benzynes</a> (4) </li> <li class="cat-item cat-item-46"> <a href="/blog/archives/category/molecules/biphenyl">biphenyl</a> (1) </li> <li class="cat-item cat-item-70"> <a href="/blog/archives/category/molecules/calixarenes">calixarenes</a> (1) </li> <li class="cat-item cat-item-33"> <a href="/blog/archives/category/molecules/carbenes">carbenes</a> (13) </li> <li class="cat-item cat-item-72 current-cat"> <a aria-current="page" href="/blog/archives/category/molecules/cyclobutadiene">cyclobutadiene</a> (4) </li> <li class="cat-item cat-item-62"> <a href="/blog/archives/category/molecules/dendralenes">dendralenes</a> (1) </li> <li class="cat-item cat-item-66"> <a href="/blog/archives/category/molecules/dewar-benzene">Dewar benzene</a> (1) </li> <li class="cat-item cat-item-39"> <a href="/blog/archives/category/molecules/diradicals">diradicals</a> (8) </li> <li class="cat-item cat-item-59"> <a href="/blog/archives/category/molecules/ephedrine">ephedrine</a> (1) </li> <li class="cat-item cat-item-37"> <a href="/blog/archives/category/molecules/ethyl-cation">ethyl cation</a> (2) </li> <li class="cat-item cat-item-90"> <a href="/blog/archives/category/molecules/fullerene">fullerene</a> (6) </li> <li class="cat-item cat-item-51"> <a href="/blog/archives/category/molecules/fulvalenes">fulvalenes</a> (1) </li> <li class="cat-item cat-item-21"> <a href="/blog/archives/category/molecules/hexacyclinol">hexacyclinol</a> (2) </li> <li class="cat-item cat-item-78"> <a href="/blog/archives/category/molecules/nanohoops">nanohoops</a> (4) </li> <li class="cat-item cat-item-41"> <a href="/blog/archives/category/molecules/non-classical">non-classical</a> (4) </li> <li class="cat-item cat-item-34"> <a href="/blog/archives/category/molecules/norbornyl-cation">norbornyl cation</a> (2) </li> <li class="cat-item cat-item-49"> <a href="/blog/archives/category/molecules/nucleic-acids">nucleic acids</a> (4) </li> <li class="cat-item cat-item-36"> <a href="/blog/archives/category/molecules/oximes">oximes</a> (1) </li> <li class="cat-item cat-item-75"> <a href="/blog/archives/category/molecules/phenyloxenium">phenyloxenium</a> (1) </li> <li class="cat-item cat-item-8"> <a href="/blog/archives/category/molecules/polycyclic-aromatics">polycyclic aromatics</a> (7) </li> <li class="cat-item cat-item-50"> <a href="/blog/archives/category/molecules/propellane">propellane</a> (2) </li> <li class="cat-item cat-item-79"> <a href="/blog/archives/category/molecules/stilbene">stilbene</a> (1) </li> <li class="cat-item cat-item-80"> <a href="/blog/archives/category/molecules/sugars">sugars</a> (5) </li> <li class="cat-item cat-item-85"> <a href="/blog/archives/category/molecules/terpenes">terpenes</a> (2) </li> <li class="cat-item cat-item-89"> <a href="/blog/archives/category/molecules/twistane">twistane</a> (1) </li> </ul> </li> <li class="cat-item cat-item-22"> <a href="/blog/archives/category/nmr">NMR</a> (40) </li> <li class="cat-item cat-item-31"> <a href="/blog/archives/category/optical-rotation">Optical Rotation</a> (16) </li> <li class="cat-item cat-item-28"> <a href="/blog/archives/category/qm-method">QM Method</a> (96) <ul class="children"> <li class="cat-item cat-item-20"> <a href="/blog/archives/category/qm-method/caspt2">CASPT2</a> (1) </li> <li class="cat-item cat-item-7"> <a href="/blog/archives/category/qm-method/dft">DFT</a> (71) </li> <li class="cat-item cat-item-45"> <a href="/blog/archives/category/qm-method/focal-point">focal point</a> (7) </li> <li class="cat-item cat-item-14"> <a href="/blog/archives/category/qm-method/g3">G3</a> (3) </li> <li class="cat-item cat-item-60"> <a href="/blog/archives/category/qm-method/mp">MP</a> (11) </li> </ul> </li> <li class="cat-item cat-item-56"> <a href="/blog/archives/category/reactions">Reactions</a> (83) <ul class="children"> <li class="cat-item cat-item-13"> <a href="/blog/archives/category/reactions/12-addition">1,2-addition</a> (1) </li> <li class="cat-item cat-item-35"> <a href="/blog/archives/category/reactions/aldol">aldol</a> (4) </li> <li class="cat-item cat-item-32"> <a href="/blog/archives/category/reactions/bergman-cyclization">Bergman cyclization</a> (6) </li> <li class="cat-item cat-item-44"> <a href="/blog/archives/category/reactions/claisen-rearrangement">Claisen rearrangement</a> (2) </li> <li class="cat-item cat-item-10"> <a href="/blog/archives/category/reactions/cope-rearrangement">Cope Rearrangement</a> (5) </li> <li class="cat-item cat-item-69"> <a href="/blog/archives/category/reactions/cycloadditions">cycloadditions</a> (12) </li> <li class="cat-item cat-item-23"> <a href="/blog/archives/category/reactions/diels-alder">Diels-Alder</a> (26) </li> <li class="cat-item cat-item-47"> <a href="/blog/archives/category/reactions/electrocyclization">electrocyclization</a> (11) </li> <li class="cat-item cat-item-76"> <a href="/blog/archives/category/reactions/electrophilic-aromatic-substitution">electrophilic aromatic substitution</a> (1) </li> <li class="cat-item cat-item-5"> <a href="/blog/archives/category/reactions/ene-reaction">ene reaction</a> (1) </li> <li class="cat-item cat-item-52"> <a href="/blog/archives/category/reactions/hajos-parrish-reaction">Hajos-Parrish Reaction</a> (1) </li> <li class="cat-item cat-item-61"> <a href="/blog/archives/category/reactions/mannich">Mannich</a> (2) </li> <li class="cat-item cat-item-64"> <a href="/blog/archives/category/reactions/michael-addition">Michael addition</a> (5) </li> <li class="cat-item cat-item-40"> <a href="/blog/archives/category/reactions/ozonolysis">ozonolysis</a> (1) </li> <li class="cat-item cat-item-43"> <a href="/blog/archives/category/reactions/proton-transfer">proton transfer</a> (1) </li> <li class="cat-item cat-item-38"> <a href="/blog/archives/category/reactions/pseudopericyclic">pseudopericyclic</a> (4) </li> <li class="cat-item cat-item-63"> <a href="/blog/archives/category/reactions/strecker">Strecker</a> (1) </li> <li class="cat-item cat-item-24"> <a href="/blog/archives/category/reactions/substitution">Substitution</a> (6) </li> <li class="cat-item cat-item-93"> <a href="/blog/archives/category/reactions/wittig">Wittig</a> (1) </li> </ul> </li> <li class="cat-item cat-item-87"> <a href="/blog/archives/category/second-edition">Second Edition</a> (3) </li> <li class="cat-item cat-item-11"> <a href="/blog/archives/category/solvation">Solvation</a> (17) </li> <li class="cat-item cat-item-77"> <a href="/blog/archives/category/stereochemistry">Stereochemistry</a> (2) </li> <li class="cat-item cat-item-68"> <a href="/blog/archives/category/stereoinduction">stereoinduction</a> (4) </li> <li class="cat-item cat-item-71"> <a href="/blog/archives/category/tunneling">Tunneling</a> (26) </li> <li class="cat-item cat-item-1"> <a href="/blog/archives/category/uncategorized">Uncategorized</a> (57) </li> <li class="cat-item cat-item-82"> <a href="/blog/archives/category/vibrational-frequencies">vibrational frequencies</a> (3) </li> </ul> </li> <li class="box"> <h2> Monthly </h2> <ul> <li><a href="/blog/archives/date/2019/06">June 2019</a></li> <li><a href="/blog/archives/date/2019/04">April 2019</a></li> <li><a href="/blog/archives/date/2019/03">March 2019</a></li> <li><a href="/blog/archives/date/2019/02">February 2019</a></li> <li><a href="/blog/archives/date/2019/01">January 2019</a></li> <li><a href="/blog/archives/date/2018/12">December 2018</a></li> <li><a href="/blog/archives/date/2018/11">November 2018</a></li> <li><a href="/blog/archives/date/2018/10">October 2018</a></li> <li><a href="/blog/archives/date/2018/09">September 2018</a></li> <li><a href="/blog/archives/date/2018/08">August 2018</a></li> <li><a href="/blog/archives/date/2018/07">July 2018</a></li> <li><a href="/blog/archives/date/2018/06">June 2018</a></li> <li><a href="/blog/archives/date/2018/05">May 2018</a></li> <li><a href="/blog/archives/date/2018/04">April 2018</a></li> <li><a href="/blog/archives/date/2018/03">March 2018</a></li> <li><a href="/blog/archives/date/2018/02">February 2018</a></li> <li><a href="/blog/archives/date/2018/01">January 2018</a></li> <li><a href="/blog/archives/date/2017/12">December 2017</a></li> <li><a href="/blog/archives/date/2017/11">November 2017</a></li> <li><a href="/blog/archives/date/2017/10">October 2017</a></li> <li><a href="/blog/archives/date/2017/09">September 2017</a></li> <li><a href="/blog/archives/date/2017/08">August 2017</a></li> <li><a href="/blog/archives/date/2017/07">July 2017</a></li> <li><a href="/blog/archives/date/2017/06">June 2017</a></li> <li><a href="/blog/archives/date/2017/05">May 2017</a></li> <li><a href="/blog/archives/date/2017/04">April 2017</a></li> <li><a href="/blog/archives/date/2017/03">March 2017</a></li> <li><a href="/blog/archives/date/2017/02">February 2017</a></li> <li><a href="/blog/archives/date/2017/01">January 2017</a></li> <li><a href="/blog/archives/date/2016/12">December 2016</a></li> <li><a href="/blog/archives/date/2016/11">November 2016</a></li> <li><a href="/blog/archives/date/2016/10">October 2016</a></li> <li><a href="/blog/archives/date/2016/09">September 2016</a></li> <li><a href="/blog/archives/date/2016/08">August 2016</a></li> <li><a href="/blog/archives/date/2016/07">July 2016</a></li> <li><a href="/blog/archives/date/2016/06">June 2016</a></li> <li><a href="/blog/archives/date/2016/05">May 2016</a></li> <li><a href="/blog/archives/date/2016/04">April 2016</a></li> <li><a href="/blog/archives/date/2016/03">March 2016</a></li> <li><a href="/blog/archives/date/2016/02">February 2016</a></li> <li><a href="/blog/archives/date/2016/01">January 2016</a></li> <li><a href="/blog/archives/date/2015/12">December 2015</a></li> <li><a href="/blog/archives/date/2015/11">November 2015</a></li> <li><a href="/blog/archives/date/2015/10">October 2015</a></li> <li><a href="/blog/archives/date/2015/09">September 2015</a></li> <li><a href="/blog/archives/date/2015/08">August 2015</a></li> <li><a href="/blog/archives/date/2015/07">July 2015</a></li> <li><a href="/blog/archives/date/2015/06">June 2015</a></li> <li><a href="/blog/archives/date/2015/05">May 2015</a></li> <li><a href="/blog/archives/date/2015/04">April 2015</a></li> <li><a href="/blog/archives/date/2015/03">March 2015</a></li> <li><a href="/blog/archives/date/2015/02">February 2015</a></li> <li><a href="/blog/archives/date/2015/01">January 2015</a></li> <li><a href="/blog/archives/date/2014/12">December 2014</a></li> <li><a href="/blog/archives/date/2014/11">November 2014</a></li> <li><a href="/blog/archives/date/2014/10">October 2014</a></li> <li><a href="/blog/archives/date/2014/09">September 2014</a></li> <li><a href="/blog/archives/date/2014/08">August 2014</a></li> <li><a href="/blog/archives/date/2014/07">July 2014</a></li> <li><a href="/blog/archives/date/2014/06">June 2014</a></li> <li><a href="/blog/archives/date/2014/05">May 2014</a></li> <li><a href="/blog/archives/date/2014/04">April 2014</a></li> <li><a href="/blog/archives/date/2014/03">March 2014</a></li> <li><a href="/blog/archives/date/2014/02">February 2014</a></li> <li><a href="/blog/archives/date/2014/01">January 2014</a></li> <li><a href="/blog/archives/date/2013/12">December 2013</a></li> <li><a href="/blog/archives/date/2013/11">November 2013</a></li> <li><a href="/blog/archives/date/2013/10">October 2013</a></li> <li><a href="/blog/archives/date/2013/09">September 2013</a></li> <li><a href="/blog/archives/date/2013/08">August 2013</a></li> <li><a href="/blog/archives/date/2013/07">July 2013</a></li> <li><a href="/blog/archives/date/2013/06">June 2013</a></li> <li><a href="/blog/archives/date/2013/05">May 2013</a></li> <li><a href="/blog/archives/date/2013/04">April 2013</a></li> <li><a href="/blog/archives/date/2013/03">March 2013</a></li> <li><a href="/blog/archives/date/2013/02">February 2013</a></li> <li><a href="/blog/archives/date/2013/01">January 2013</a></li> <li><a href="/blog/archives/date/2012/12">December 2012</a></li> <li><a href="/blog/archives/date/2012/11">November 2012</a></li> <li><a href="/blog/archives/date/2012/10">October 2012</a></li> <li><a href="/blog/archives/date/2012/09">September 2012</a></li> <li><a href="/blog/archives/date/2012/08">August 2012</a></li> <li><a href="/blog/archives/date/2012/07">July 2012</a></li> <li><a href="/blog/archives/date/2012/06">June 2012</a></li> <li><a href="/blog/archives/date/2012/05">May 2012</a></li> <li><a href="/blog/archives/date/2012/04">April 2012</a></li> <li><a href="/blog/archives/date/2012/03">March 2012</a></li> <li><a href="/blog/archives/date/2012/02">February 2012</a></li> <li><a href="/blog/archives/date/2012/01">January 2012</a></li> <li><a href="/blog/archives/date/2011/12">December 2011</a></li> <li><a href="/blog/archives/date/2011/11">November 2011</a></li> <li><a href="/blog/archives/date/2011/10">October 2011</a></li> <li><a href="/blog/archives/date/2011/09">September 2011</a></li> <li><a href="/blog/archives/date/2011/08">August 2011</a></li> <li><a href="/blog/archives/date/2011/07">July 2011</a></li> <li><a href="/blog/archives/date/2011/06">June 2011</a></li> <li><a href="/blog/archives/date/2011/05">May 2011</a></li> <li><a href="/blog/archives/date/2011/04">April 2011</a></li> <li><a href="/blog/archives/date/2011/03">March 2011</a></li> <li><a href="/blog/archives/date/2011/02">February 2011</a></li> <li><a href="/blog/archives/date/2011/01">January 2011</a></li> <li><a href="/blog/archives/date/2010/12">December 2010</a></li> <li><a href="/blog/archives/date/2010/11">November 2010</a></li> <li><a href="/blog/archives/date/2010/10">October 2010</a></li> <li><a href="/blog/archives/date/2010/09">September 2010</a></li> <li><a href="/blog/archives/date/2010/08">August 2010</a></li> <li><a href="/blog/archives/date/2010/07">July 2010</a></li> <li><a href="/blog/archives/date/2010/06">June 2010</a></li> <li><a href="/blog/archives/date/2010/05">May 2010</a></li> <li><a href="/blog/archives/date/2010/04">April 2010</a></li> <li><a href="/blog/archives/date/2010/03">March 2010</a></li> <li><a href="/blog/archives/date/2010/02">February 2010</a></li> <li><a href="/blog/archives/date/2010/01">January 2010</a></li> <li><a href="/blog/archives/date/2009/12">December 2009</a></li> <li><a href="/blog/archives/date/2009/11">November 2009</a></li> <li><a href="/blog/archives/date/2009/10">October 2009</a></li> <li><a href="/blog/archives/date/2009/09">September 2009</a></li> <li><a href="/blog/archives/date/2009/08">August 2009</a></li> <li><a href="/blog/archives/date/2009/07">July 2009</a></li> <li><a href="/blog/archives/date/2009/06">June 2009</a></li> <li><a href="/blog/archives/date/2009/05">May 2009</a></li> <li><a href="/blog/archives/date/2009/04">April 2009</a></li> <li><a href="/blog/archives/date/2009/03">March 2009</a></li> <li><a href="/blog/archives/date/2009/02">February 2009</a></li> <li><a href="/blog/archives/date/2009/01">January 2009</a></li> <li><a href="/blog/archives/date/2008/12">December 2008</a></li> <li><a href="/blog/archives/date/2008/11">November 2008</a></li> <li><a href="/blog/archives/date/2008/10">October 2008</a></li> <li><a href="/blog/archives/date/2008/09">September 2008</a></li> <li><a href="/blog/archives/date/2008/08">August 2008</a></li> <li><a href="/blog/archives/date/2008/07">July 2008</a></li> <li><a href="/blog/archives/date/2008/06">June 2008</a></li> <li><a href="/blog/archives/date/2008/05">May 2008</a></li> <li><a href="/blog/archives/date/2008/04">April 2008</a></li> <li><a href="/blog/archives/date/2008/03">March 2008</a></li> <li><a href="/blog/archives/date/2008/02">February 2008</a></li> <li><a href="/blog/archives/date/2008/01">January 2008</a></li> <li><a href="/blog/archives/date/2007/12">December 2007</a></li> <li><a href="/blog/archives/date/2007/11">November 2007</a></li> <li><a href="/blog/archives/date/2007/10">October 2007</a></li> <li><a href="/blog/archives/date/2007/09">September 2007</a></li> <li><a href="/blog/archives/date/2007/08">August 2007</a></li> <li><a href="/blog/archives/date/2007/07">July 2007</a></li> </ul> </li> </ul> <a rel="license" href="https://creativecommons.org/licenses/by-nd/3.0/"> <img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-nd/3.0/88x31.png"> </a> <br>This work is licensed under a <a rel="license" href="https://creativecommons.org/licenses/by-nd/3.0/">Creative Commons Attribution-No Derivative Works 3.0 Unported License</a>. </div>  <div class="clear"></div> 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