CINXE.COM

<!DOCTYPE html> <html class="client-nojs vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-sticky-header-enabled vector-toc-available" lang="en" dir="ltr"> <head> <meta charset="UTF-8"> <title>Hückel's rule - Wikipedia</title> <script>(function(){var className="client-js vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-sticky-header-enabled vector-toc-available";var cookie=document.cookie.match(/(?:^|; )enwikimwclientpreferences=([^;]+)/);if(cookie){cookie[1].split('%2C').forEach(function(pref){className=className.replace(new RegExp('(^| )'+pref.replace(/-clientpref-\w+$|[^\w-]+/g,'')+'-clientpref-\\w+( |$)'),'$1'+pref+'$2');});}document.documentElement.className=className;}());RLCONF={"wgBreakFrames":false,"wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy","wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgRequestId":"96d19110-5c9f-4b47-bb29-9264ed258f96","wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"Hückel's_rule","wgTitle":"Hückel's rule","wgCurRevisionId":1276109541,"wgRevisionId":1276109541,"wgArticleId":862361,"wgIsArticle":true,"wgIsRedirect":false,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["Articles with short description","Short description matches Wikidata","Physical organic chemistry","Rules of thumb"],"wgPageViewLanguage":"en","wgPageContentLanguage":"en","wgPageContentModel":"wikitext","wgRelevantPageName":"Hückel's_rule","wgRelevantArticleId":862361,"wgIsProbablyEditable":true,"wgRelevantPageIsProbablyEditable":true,"wgRestrictionEdit":[],"wgRestrictionMove":[],"wgNoticeProject":"wikipedia","wgCiteReferencePreviewsActive":false,"wgFlaggedRevsParams":{"tags":{"status":{"levels":1}}},"wgMediaViewerOnClick":true,"wgMediaViewerEnabledByDefault":true,"wgPopupsFlags":0,"wgVisualEditor":{"pageLanguageCode":"en","pageLanguageDir":"ltr","pageVariantFallbacks":"en"},"wgMFDisplayWikibaseDescriptions":{"search":true,"watchlist":true,"tagline":false,"nearby":true},"wgWMESchemaEditAttemptStepOversample":false,"wgWMEPageLength":10000,"wgEditSubmitButtonLabelPublish":true,"wgULSPosition":"interlanguage","wgULSisCompactLinksEnabled":false,"wgVector2022LanguageInHeader":true,"wgULSisLanguageSelectorEmpty":false,"wgWikibaseItemId":"Q534307","wgCheckUserClientHintsHeadersJsApi":["brands","architecture","bitness","fullVersionList","mobile","model","platform","platformVersion"],"GEHomepageSuggestedEditsEnableTopics":true,"wgGETopicsMatchModeEnabled":false,"wgGELevelingUpEnabledForUser":false}; RLSTATE={"ext.globalCssJs.user.styles":"ready","site.styles":"ready","user.styles":"ready","ext.globalCssJs.user":"ready","user":"ready","user.options":"loading","ext.cite.styles":"ready","skins.vector.search.codex.styles":"ready","skins.vector.styles":"ready","skins.vector.icons":"ready","jquery.makeCollapsible.styles":"ready","ext.wikimediamessages.styles":"ready","ext.visualEditor.desktopArticleTarget.noscript":"ready","ext.uls.interlanguage":"ready","wikibase.client.init":"ready"};RLPAGEMODULES=["ext.cite.ux-enhancements","mediawiki.page.media","site","mediawiki.page.ready","jquery.makeCollapsible","mediawiki.toc","skins.vector.js","ext.centralNotice.geoIP","ext.centralNotice.startUp","ext.gadget.ReferenceTooltips","ext.gadget.switcher","ext.urlShortener.toolbar","ext.centralauth.centralautologin","mmv.bootstrap","ext.popups","ext.visualEditor.desktopArticleTarget.init","ext.visualEditor.targetLoader","ext.echo.centralauth","ext.eventLogging","ext.wikimediaEvents","ext.navigationTiming","ext.uls.interface","ext.cx.eventlogging.campaigns","ext.cx.uls.quick.actions","wikibase.client.vector-2022","ext.checkUser.clientHints","ext.quicksurveys.init","ext.growthExperiments.SuggestedEditSession"];</script> <script>(RLQ=window.RLQ||[]).push(function(){mw.loader.impl(function(){return["user.options@12s5i",function($,jQuery,require,module){mw.user.tokens.set({"patrolToken":"+\\","watchToken":"+\\","csrfToken":"+\\"}); }];});});</script> <link rel="stylesheet" href="/w/load.php?lang=en&modules=ext.cite.styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediamessages.styles%7Cjquery.makeCollapsible.styles%7Cskins.vector.icons%2Cstyles%7Cskins.vector.search.codex.styles%7Cwikibase.client.init&only=styles&skin=vector-2022"> <script async="" src="/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=vector-2022"></script> <meta name="ResourceLoaderDynamicStyles" content=""> <link rel="stylesheet" href="/w/load.php?lang=en&modules=site.styles&only=styles&skin=vector-2022"> <meta name="generator" content="MediaWiki 1.44.0-wmf.21"> <meta name="referrer" content="origin"> <meta name="referrer" content="origin-when-cross-origin"> <meta name="robots" content="max-image-preview:standard"> <meta name="format-detection" content="telephone=no"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/1200px-Benzol.svg.png"> <meta property="og:image:width" content="1200"> <meta property="og:image:height" content="1366"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/800px-Benzol.svg.png"> <meta property="og:image:width" content="800"> <meta property="og:image:height" content="911"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/640px-Benzol.svg.png"> <meta property="og:image:width" content="640"> <meta property="og:image:height" content="729"> <meta name="viewport" content="width=1120"> <meta property="og:title" content="Hückel's rule - Wikipedia"> <meta property="og:type" content="website"> <link rel="preconnect" href="//upload.wikimedia.org"> <link rel="alternate" media="only screen and (max-width: 640px)" href="//en.m.wikipedia.org/wiki/H%C3%BCckel%27s_rule"> <link rel="alternate" type="application/x-wiki" title="Edit this page" href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit"> <link rel="apple-touch-icon" href="/static/apple-touch/wikipedia.png"> <link rel="icon" href="/static/favicon/wikipedia.ico"> <link rel="search" type="application/opensearchdescription+xml" href="/w/rest.php/v1/search" title="Wikipedia (en)"> <link rel="EditURI" type="application/rsd+xml" href="//en.wikipedia.org/w/api.php?action=rsd"> <link rel="canonical" href="https://en.wikipedia.org/wiki/H%C3%BCckel%27s_rule"> <link rel="license" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en"> <link rel="alternate" type="application/atom+xml" title="Wikipedia Atom feed" href="/w/index.php?title=Special:RecentChanges&feed=atom"> <link rel="dns-prefetch" href="//meta.wikimedia.org" /> <link rel="dns-prefetch" href="login.wikimedia.org"> </head> <body class="skin--responsive skin-vector skin-vector-search-vue mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject mw-editable page-Hückel_s_rule rootpage-Hückel_s_rule skin-vector-2022 action-view"><a class="mw-jump-link" href="#bodyContent">Jump to content</a> <div class="vector-header-container"> <header class="vector-header mw-header"> <div class="vector-header-start"> <nav class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-dropdown" class="vector-dropdown vector-main-menu-dropdown vector-button-flush-left vector-button-flush-right" title="Main menu" > <input type="checkbox" id="vector-main-menu-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-main-menu-dropdown" class="vector-dropdown-checkbox " aria-label="Main menu" > <label id="vector-main-menu-dropdown-label" for="vector-main-menu-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-menu mw-ui-icon-wikimedia-menu"></span> <span class="vector-dropdown-label-text">Main menu</span> </label> <div class="vector-dropdown-content"> <div id="vector-main-menu-unpinned-container" class="vector-unpinned-container"> <div id="vector-main-menu" class="vector-main-menu vector-pinnable-element"> <div class="vector-pinnable-header vector-main-menu-pinnable-header vector-pinnable-header-unpinned" data-feature-name="main-menu-pinned" data-pinnable-element-id="vector-main-menu" data-pinned-container-id="vector-main-menu-pinned-container" data-unpinned-container-id="vector-main-menu-unpinned-container" > <div class="vector-pinnable-header-label">Main menu</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-main-menu.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-main-menu.unpin">hide</button> </div> <div id="p-navigation" class="vector-menu mw-portlet mw-portlet-navigation" > <div class="vector-menu-heading"> Navigation </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-mainpage-description" class="mw-list-item"><a href="/wiki/Main_Page" title="Visit the main page [z]" accesskey="z"><span>Main page</span></a></li><li id="n-contents" class="mw-list-item"><a href="/wiki/Wikipedia:Contents" title="Guides to browsing Wikipedia"><span>Contents</span></a></li><li id="n-currentevents" class="mw-list-item"><a href="/wiki/Portal:Current_events" title="Articles related to current events"><span>Current events</span></a></li><li id="n-randompage" class="mw-list-item"><a href="/wiki/Special:Random" title="Visit a randomly selected article [x]" accesskey="x"><span>Random article</span></a></li><li id="n-aboutsite" class="mw-list-item"><a href="/wiki/Wikipedia:About" title="Learn about Wikipedia and how it works"><span>About Wikipedia</span></a></li><li id="n-contactpage" class="mw-list-item"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us" title="How to contact Wikipedia"><span>Contact us</span></a></li> </ul> </div> </div> <div id="p-interaction" class="vector-menu mw-portlet mw-portlet-interaction" > <div class="vector-menu-heading"> Contribute </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-help" class="mw-list-item"><a href="/wiki/Help:Contents" title="Guidance on how to use and edit Wikipedia"><span>Help</span></a></li><li id="n-introduction" class="mw-list-item"><a href="/wiki/Help:Introduction" title="Learn how to edit Wikipedia"><span>Learn to edit</span></a></li><li id="n-portal" class="mw-list-item"><a href="/wiki/Wikipedia:Community_portal" title="The hub for editors"><span>Community portal</span></a></li><li id="n-recentchanges" class="mw-list-item"><a href="/wiki/Special:RecentChanges" title="A list of recent changes to Wikipedia [r]" accesskey="r"><span>Recent changes</span></a></li><li id="n-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_upload_wizard" title="Add images or other media for use on Wikipedia"><span>Upload file</span></a></li><li id="n-specialpages" class="mw-list-item"><a href="/wiki/Special:SpecialPages"><span>Special pages</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> <a href="/wiki/Main_Page" class="mw-logo"> <img class="mw-logo-icon" src="/static/images/icons/wikipedia.png" alt="" aria-hidden="true" height="50" width="50"> <span class="mw-logo-container skin-invert"> <img class="mw-logo-wordmark" alt="Wikipedia" src="/static/images/mobile/copyright/wikipedia-wordmark-en.svg" style="width: 7.5em; height: 1.125em;"> <img class="mw-logo-tagline" alt="The Free Encyclopedia" src="/static/images/mobile/copyright/wikipedia-tagline-en.svg" width="117" height="13" style="width: 7.3125em; height: 0.8125em;"> </span> </a> </div> <div class="vector-header-end"> <div id="p-search" role="search" class="vector-search-box-vue vector-search-box-collapses vector-search-box-show-thumbnail vector-search-box-auto-expand-width vector-search-box"> <a href="/wiki/Special:Search" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only search-toggle" title="Search Wikipedia [f]" accesskey="f"><span class="vector-icon mw-ui-icon-search mw-ui-icon-wikimedia-search"></span> <span>Search</span> </a> <div class="vector-typeahead-search-container"> <div class="cdx-typeahead-search cdx-typeahead-search--show-thumbnail cdx-typeahead-search--auto-expand-width"> <form action="/w/index.php" id="searchform" class="cdx-search-input cdx-search-input--has-end-button"> <div id="simpleSearch" class="cdx-search-input__input-wrapper" data-search-loc="header-moved"> <div class="cdx-text-input cdx-text-input--has-start-icon"> <input class="cdx-text-input__input" type="search" name="search" placeholder="Search Wikipedia" aria-label="Search Wikipedia" autocapitalize="sentences" title="Search Wikipedia [f]" accesskey="f" id="searchInput" > <span class="cdx-text-input__icon cdx-text-input__start-icon"></span> </div> <input type="hidden" name="title" value="Special:Search"> </div> <button class="cdx-button cdx-search-input__end-button">Search</button> </form> </div> </div> </div> <nav class="vector-user-links vector-user-links-wide" aria-label="Personal tools"> <div class="vector-user-links-main"> <div id="p-vector-user-menu-preferences" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-userpage" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-dropdown" class="vector-dropdown " title="Change the appearance of the page's font size, width, and color" > <input type="checkbox" id="vector-appearance-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-appearance-dropdown" class="vector-dropdown-checkbox " aria-label="Appearance" > <label id="vector-appearance-dropdown-label" for="vector-appearance-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-appearance mw-ui-icon-wikimedia-appearance"></span> <span class="vector-dropdown-label-text">Appearance</span> </label> <div class="vector-dropdown-content"> <div id="vector-appearance-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <div id="p-vector-user-menu-notifications" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-overflow" class="vector-menu mw-portlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="https://donate.wikimedia.org/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en" class=""><span>Donate</span></a> </li> <li id="pt-createaccount-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:CreateAccount&returnto=H%C3%BCckel%27s+rule" title="You are encouraged to create an account and log in; however, it is not mandatory" class=""><span>Create account</span></a> </li> <li id="pt-login-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:UserLogin&returnto=H%C3%BCckel%27s+rule" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o" class=""><span>Log in</span></a> </li> </ul> </div> </div> </div> <div id="vector-user-links-dropdown" class="vector-dropdown vector-user-menu vector-button-flush-right vector-user-menu-logged-out" title="Log in and more options" > <input type="checkbox" id="vector-user-links-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-user-links-dropdown" class="vector-dropdown-checkbox " aria-label="Personal tools" > <label id="vector-user-links-dropdown-label" for="vector-user-links-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-ellipsis mw-ui-icon-wikimedia-ellipsis"></span> <span class="vector-dropdown-label-text">Personal tools</span> </label> <div class="vector-dropdown-content"> <div id="p-personal" class="vector-menu mw-portlet mw-portlet-personal user-links-collapsible-item" title="User menu" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport" class="user-links-collapsible-item mw-list-item"><a href="https://donate.wikimedia.org/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en"><span>Donate</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:CreateAccount&returnto=H%C3%BCckel%27s+rule" title="You are encouraged to create an account and log in; however, it is not mandatory"><span class="vector-icon mw-ui-icon-userAdd mw-ui-icon-wikimedia-userAdd"></span> <span>Create account</span></a></li><li id="pt-login" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:UserLogin&returnto=H%C3%BCckel%27s+rule" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Log in</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Pages for logged out editors <a href="/wiki/Help:Introduction" aria-label="Learn more about editing"><span>learn more</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Special:MyContributions" title="A list of edits made from this IP address [y]" accesskey="y"><span>Contributions</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Special:MyTalk" title="Discussion about edits from this IP address [n]" accesskey="n"><span>Talk</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> <div class="vector-sticky-pinned-container"> <nav id="mw-panel-toc" aria-label="Contents" data-event-name="ui.sidebar-toc" class="mw-table-of-contents-container vector-toc-landmark"> <div id="vector-toc-pinned-container" class="vector-pinned-container"> <div id="vector-toc" class="vector-toc vector-pinnable-element"> <div class="vector-pinnable-header vector-toc-pinnable-header vector-pinnable-header-pinned" data-feature-name="toc-pinned" data-pinnable-element-id="vector-toc" > <h2 class="vector-pinnable-header-label">Contents</h2> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-Monocyclic_hydrocarbons" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Monocyclic_hydrocarbons"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>Monocyclic hydrocarbons</span> </div> </a> <ul id="toc-Monocyclic_hydrocarbons-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Heteroatoms" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Heteroatoms"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Heteroatoms</span> </div> </a> <ul id="toc-Heteroatoms-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Polycyclic_hydrocarbons" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Polycyclic_hydrocarbons"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Polycyclic hydrocarbons</span> </div> </a> <ul id="toc-Polycyclic_hydrocarbons-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Three-dimensional_rule" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Three-dimensional_rule"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Three-dimensional rule</span> </div> </a> <ul id="toc-Three-dimensional_rule-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Hückel's rule</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 21 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-21" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">21 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D9%82%D8%A7%D8%B9%D8%AF%D8%A9_%D9%87%D9%88%D9%83%D9%84" title="قاعدة هوكل – Arabic" lang="ar" hreflang="ar" data-title="قاعدة هوكل" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Regla_de_H%C3%BCckel" title="Regla de Hückel – Catalan" lang="ca" hreflang="ca" data-title="Regla de Hückel" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/H%C3%BCckel-Regel" title="Hückel-Regel – German" lang="de" hreflang="de" data-title="Hückel-Regel" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Regla_de_H%C3%BCckel" title="Regla de Hückel – Spanish" lang="es" hreflang="es" data-title="Regla de Hückel" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/H%C3%BCckelen_arau" title="Hückelen arau – Basque" lang="eu" hreflang="eu" data-title="Hückelen arau" 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/%D9%82%D8%A7%D8%B9%D8%AF%D9%87_%D9%87%D9%88%DA%A9%D9%84" title="قاعده هوکل – Persian" lang="fa" hreflang="fa" data-title="قاعده هوکل" 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/R%C3%A8gle_de_H%C3%BCckel" title="Règle de Hückel – French" lang="fr" hreflang="fr" data-title="Règle de Hückel" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%ED%9C%98%EC%BC%88_%EA%B7%9C%EC%B9%99" title="휘켈 규칙 – Korean" lang="ko" hreflang="ko" data-title="휘켈 규칙" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Aturan_H%C3%BCckel" title="Aturan Hückel – Indonesian" lang="id" hreflang="id" data-title="Aturan Hückel" 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-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Regola_di_H%C3%BCckel" title="Regola di Hückel – Italian" lang="it" hreflang="it" data-title="Regola di Hückel" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%A5%D0%B8%D0%BA%D0%B5%D0%BB%D0%BE%D0%B2%D0%BE_%D0%BF%D1%80%D0%B0%D0%B2%D0%B8%D0%BB%D0%BE" title="Хикелово правило – Macedonian" lang="mk" hreflang="mk" data-title="Хикелово правило" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Regel_van_H%C3%BCckel" title="Regel van Hückel – Dutch" lang="nl" hreflang="nl" data-title="Regel van Hückel" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%83%92%E3%83%A5%E3%83%83%E3%82%B1%E3%83%AB%E5%89%87" title="ヒュッケル則 – Japanese" lang="ja" hreflang="ja" data-title="ヒュッケル則" 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-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Regu%C5%82a_H%C3%BCckla" title="Reguła Hückla – Polish" lang="pl" hreflang="pl" data-title="Reguła Hückla" 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/Regra_de_H%C3%BCckel" title="Regra de Hückel – Portuguese" lang="pt" hreflang="pt" data-title="Regra de Hückel" 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/Regula_lui_H%C3%BCckel" title="Regula lui Hückel – Romanian" lang="ro" hreflang="ro" data-title="Regula lui Hückel" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/H%C3%BCckel%27s_rule" title="Hückel's rule – Simple English" lang="en-simple" hreflang="en-simple" data-title="Hückel's rule" 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-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/H%C3%BCcklovo_pravilo" title="Hücklovo pravilo – Slovenian" lang="sl" hreflang="sl" data-title="Hücklovo pravilo" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9F%D1%80%D0%B0%D0%B2%D0%B8%D0%BB%D0%BE_%D0%93%D1%8E%D0%BA%D0%BA%D0%B5%D0%BB%D1%8F" title="Правило Гюккеля – Ukrainian" lang="uk" hreflang="uk" data-title="Правило Гюккеля" 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/Quy_t%E1%BA%AFc_H%C3%BCckel" title="Quy tắc Hückel – Vietnamese" lang="vi" hreflang="vi" data-title="Quy tắc Hückel" 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-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E4%BC%91%E5%85%8B%E5%B0%94%E6%B3%95%E5%88%99" title="休克尔法则 – Chinese" lang="zh" hreflang="zh" data-title="休克尔法则" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q534307#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/H%C3%BCckel%27s_rule" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:H%C3%BCckel%27s_rule" rel="discussion" title="Discuss improvements to the content page [t]" accesskey="t"><span>Talk</span></a></li> </ul> </div> </div> <div id="vector-variants-dropdown" class="vector-dropdown emptyPortlet" > <input type="checkbox" id="vector-variants-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-variants-dropdown" class="vector-dropdown-checkbox " aria-label="Change language variant" > <label id="vector-variants-dropdown-label" for="vector-variants-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">English</span> </label> <div class="vector-dropdown-content"> <div id="p-variants" class="vector-menu mw-portlet mw-portlet-variants emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> </div> </div> </nav> </div> <div id="right-navigation" class="vector-collapsible"> <nav aria-label="Views"> <div id="p-views" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-views" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-view" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/H%C3%BCckel%27s_rule"><span>Read</span></a></li><li id="ca-edit" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-history" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=history" title="Past revisions of this page [h]" accesskey="h"><span>View history</span></a></li> </ul> </div> </div> </nav> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-dropdown" class="vector-dropdown vector-page-tools-dropdown" > <input type="checkbox" id="vector-page-tools-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-tools-dropdown" class="vector-dropdown-checkbox " aria-label="Tools" > <label id="vector-page-tools-dropdown-label" for="vector-page-tools-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">Tools</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-tools-unpinned-container" class="vector-unpinned-container"> <div id="vector-page-tools" class="vector-page-tools vector-pinnable-element"> <div class="vector-pinnable-header vector-page-tools-pinnable-header vector-pinnable-header-unpinned" data-feature-name="page-tools-pinned" data-pinnable-element-id="vector-page-tools" data-pinned-container-id="vector-page-tools-pinned-container" data-unpinned-container-id="vector-page-tools-unpinned-container" > <div class="vector-pinnable-header-label">Tools</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-page-tools.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-page-tools.unpin">hide</button> </div> <div id="p-cactions" class="vector-menu mw-portlet mw-portlet-cactions emptyPortlet vector-has-collapsible-items" title="More options" > <div class="vector-menu-heading"> Actions </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-more-view" class="selected vector-more-collapsible-item mw-list-item"><a href="/wiki/H%C3%BCckel%27s_rule"><span>Read</span></a></li><li id="ca-more-edit" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-more-history" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=history"><span>View history</span></a></li> </ul> </div> </div> <div id="p-tb" class="vector-menu mw-portlet mw-portlet-tb" > <div class="vector-menu-heading"> General </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-whatlinkshere" class="mw-list-item"><a href="/wiki/Special:WhatLinksHere/H%C3%BCckel%27s_rule" title="List of all English Wikipedia pages containing links to this page [j]" accesskey="j"><span>What links here</span></a></li><li id="t-recentchangeslinked" class="mw-list-item"><a href="/wiki/Special:RecentChangesLinked/H%C3%BCckel%27s_rule" rel="nofollow" title="Recent changes in pages linked from this page [k]" accesskey="k"><span>Related changes</span></a></li><li id="t-upload" class="mw-list-item"><a href="//en.wikipedia.org/wiki/Wikipedia:File_Upload_Wizard" title="Upload files [u]" accesskey="u"><span>Upload file</span></a></li><li id="t-permalink" class="mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&oldid=1276109541" title="Permanent link to this revision of this page"><span>Permanent link</span></a></li><li id="t-info" class="mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=info" title="More information about this page"><span>Page information</span></a></li><li id="t-cite" class="mw-list-item"><a href="/w/index.php?title=Special:CiteThisPage&page=H%C3%BCckel%27s_rule&id=1276109541&wpFormIdentifier=titleform" title="Information on how to cite this page"><span>Cite this page</span></a></li><li id="t-urlshortener" class="mw-list-item"><a href="/w/index.php?title=Special:UrlShortener&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FH%25C3%25BCckel%2527s_rule"><span>Get shortened URL</span></a></li><li id="t-urlshortener-qrcode" class="mw-list-item"><a href="/w/index.php?title=Special:QrCode&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FH%25C3%25BCckel%2527s_rule"><span>Download QR code</span></a></li> </ul> </div> </div> <div id="p-coll-print_export" class="vector-menu mw-portlet mw-portlet-coll-print_export" > <div class="vector-menu-heading"> Print/export </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="coll-download-as-rl" class="mw-list-item"><a href="/w/index.php?title=Special:DownloadAsPdf&page=H%C3%BCckel%27s_rule&action=show-download-screen" title="Download this page as a PDF file"><span>Download as PDF</span></a></li><li id="t-print" class="mw-list-item"><a href="/w/index.php?title=H%C3%BCckel%27s_rule&printable=yes" title="Printable version of this page [p]" accesskey="p"><span>Printable version</span></a></li> </ul> </div> </div> <div id="p-wikibase-otherprojects" class="vector-menu mw-portlet mw-portlet-wikibase-otherprojects" > <div class="vector-menu-heading"> In other projects </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-wikibase" class="wb-otherproject-link wb-otherproject-wikibase-dataitem mw-list-item"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q534307" title="Structured data on this page hosted by Wikidata [g]" accesskey="g"><span>Wikidata item</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> </div> </div> </div> <div class="vector-column-end"> <div class="vector-sticky-pinned-container"> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-pinned-container" class="vector-pinned-container"> </div> </nav> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-pinned-container" class="vector-pinned-container"> <div id="vector-appearance" class="vector-appearance vector-pinnable-element"> <div class="vector-pinnable-header vector-appearance-pinnable-header vector-pinnable-header-pinned" data-feature-name="appearance-pinned" data-pinnable-element-id="vector-appearance" data-pinned-container-id="vector-appearance-pinned-container" data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Appearance</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Method of determining aromaticity in organic molecules</div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Benzol.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/250px-Benzol.svg.png" decoding="async" width="200" height="228" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/330px-Benzol.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/da/Benzol.svg/500px-Benzol.svg.png 2x" data-file-width="512" data-file-height="583" /></a><figcaption><a href="/wiki/Benzene" title="Benzene">Benzene</a>, the most widely recognized aromatic compound with six <a href="/wiki/Delocalize" class="mw-redirect" title="Delocalize">delocalized</a> <a href="/wiki/%CE%A0-electron" class="mw-redirect" title="Π-electron">π-electrons</a> (4<i>n</i> + 2, for <i>n</i> = 1).</figcaption></figure> <p>In <a href="/wiki/Organic_chemistry" title="Organic chemistry">organic chemistry</a>, <b>Hückel's rule</b> predicts that a <a href="/wiki/Plane_(geometry)" class="mw-redirect" title="Plane (geometry)">planar</a> <a href="/wiki/Ring_(chemistry)" title="Ring (chemistry)">ring</a> <a href="/wiki/Molecule" title="Molecule">molecule</a> will have <a href="/wiki/Aromaticity" title="Aromaticity">aromatic</a> properties if it has 4<i>n</i> + 2 <a href="/wiki/Pi_electron" class="mw-redirect" title="Pi electron">π-electrons</a>, where <i>n</i> is a non-negative <a href="/wiki/Integer" title="Integer">integer</a>. The <a href="/wiki/Quantum_mechanic" class="mw-redirect" title="Quantum mechanic">quantum mechanical</a> basis for its formulation was first worked out by physical chemist <a href="/wiki/Erich_H%C3%BCckel" title="Erich Hückel">Erich Hückel</a> in 1931.<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> The succinct expression as the 4<i>n</i> + 2 rule has been attributed to <a href="/wiki/William_von_Eggers_Doering" title="William von Eggers Doering">W. v. E. Doering</a> (1951),<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><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> although several authors were using this form at around the same time.<sup id="cite_ref-Roberts_5-0" class="reference"><a href="#cite_note-Roberts-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p><p>In agreement with the <a href="/wiki/M%C3%B6bius%E2%80%93H%C3%BCckel_concept" title="Möbius–Hückel concept">Möbius–Hückel concept</a>, a <a href="/wiki/Cyclic_compound" title="Cyclic compound">cyclic</a> ring molecule follows Hückel's rule when the number of its π-electrons equals 4<i>n</i> + 2, although clearcut examples are really only established for values of <i>n</i> = 0 up to about <i>n</i> = 6.<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> Hückel's rule was originally based on calculations using the <a href="/wiki/H%C3%BCckel_method" title="Hückel method">Hückel method</a>, although it can also be justified by considering a <a href="/wiki/Particle_in_a_ring" title="Particle in a ring">particle in a ring</a> system, by the <a href="/wiki/Linear_combination_of_atomic_orbitals_molecular_orbital_method" class="mw-redirect" title="Linear combination of atomic orbitals molecular orbital method">LCAO method</a><sup id="cite_ref-Roberts_5-1" class="reference"><a href="#cite_note-Roberts-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and by the <a href="/wiki/Pariser%E2%80%93Parr%E2%80%93Pople_method" title="Pariser–Parr–Pople method">Pariser–Parr–Pople method</a>. </p><p>Aromatic compounds are more stable than theoretically predicted using hydrogenation data of simple <a href="/wiki/Alkene" title="Alkene">alkenes</a>; the additional stability is due to the delocalized cloud of electrons, called <i><a href="/wiki/Resonance_(chemistry)" title="Resonance (chemistry)">resonance</a> energy</i>. Criteria for simple aromatics are: </p> <ol><li>the molecule must have 4<i>n</i> + 2 (a so-called "Hückel number") π electrons<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> (2, 6, 10, ...) in a <a href="/wiki/Conjugated_system" title="Conjugated system">conjugated system</a> of p orbitals (usually on sp<sup>2</sup>-<a href="/wiki/Orbital_hybridisation" title="Orbital hybridisation">hybridized</a> atoms, but sometimes sp-hybridized);</li> <li>the molecule must be (close to) planar (p orbitals must be roughly parallel and able to interact, implicit in the requirement for conjugation);</li> <li>the molecule must be cyclic (as opposed to linear);</li> <li>the molecule must have a continuous ring of p atomic orbitals (there cannot be any sp<sup>3</sup> atoms in the ring, nor do exocyclic p orbitals count).</li></ol> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Monocyclic_hydrocarbons">Monocyclic hydrocarbons</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=1" title="Edit section: Monocyclic hydrocarbons"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The rule can be used to understand the stability of completely conjugated monocyclic hydrocarbons (known as <a href="/wiki/Annulene" title="Annulene">annulenes</a>) as well as their cations and anions. The best-known example is <a href="/wiki/Benzene" title="Benzene">benzene</a> (C<sub>6</sub>H<sub>6</sub>) with a conjugated system of six π electrons, which equals 4<i>n</i> + 2 for <i>n</i> = 1. The molecule undergoes <a href="/wiki/Substitution_reaction" title="Substitution reaction">substitution reactions</a> which preserve the six π electron system rather than <a href="/wiki/Addition_reaction" title="Addition reaction">addition reactions</a> which would destroy it. The stability of this π electron system is referred to as <a href="/wiki/Aromaticity" title="Aromaticity">aromaticity</a>. Still, in most cases, catalysts are necessary for substitution reactions to occur. </p><p>The <a href="/wiki/Cyclopentadienyl_anion" title="Cyclopentadienyl anion">cyclopentadienyl anion</a> (<span class="chemf nowrap">C<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">5</sub></span></span>H<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">5</sub></span></span></span>) with six π electrons is planar and readily generated from the unusually acidic cyclopentadiene (<a href="/wiki/Acid_dissociation_constant" title="Acid dissociation constant">p<i>K</i><sub>a</sub></a> 16), while the corresponding cation with four π electrons is destabilized, being harder to generate than a typical acyclic pentadienyl cations and is thought to be antiaromatic.<sup id="cite_ref-Levine_8-0" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Similarly, the <a href="/wiki/Tropylium_cation" title="Tropylium cation">tropylium cation</a> (<span class="chemf nowrap">C<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">7</sub></span></span>H<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">7</sub></span></span></span>), also with six π electrons, is so stable compared to a typical carbocation that its salts can be crystallized from ethanol.<sup id="cite_ref-Levine_8-1" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> On the other hand, in contrast to <a href="/wiki/Cyclopentadiene" title="Cyclopentadiene">cyclopentadiene</a>, <a href="/wiki/Cycloheptatriene" title="Cycloheptatriene">cycloheptatriene</a> is not particularly acidic (p<i>K</i><sub>a</sub> 37) and the anion is considered nonaromatic. The <a href="/wiki/Cyclopropenyl_cation" class="mw-redirect" title="Cyclopropenyl cation">cyclopropenyl cation</a> (<span class="chemf nowrap">C<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">3</sub></span></span>H<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">3</sub></span></span></span>) <sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><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> and the <a href="/wiki/Triboracyclopropenyl" title="Triboracyclopropenyl">triboracyclopropenyl</a> dianion (<span class="chemf nowrap">B<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">3</sub></span></span>H<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">2–</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">3</sub></span></span></span>) are considered examples of a two π electron system, which are stabilized relative to the open system, despite the <a href="/wiki/Ring_strain" title="Ring strain">angle strain</a> imposed by the 60° bond angles.<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><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> </p><p>Planar ring molecules with 4<i>n</i> π electrons do not obey Hückel's rule, and theory predicts that they are less stable and have <a href="/wiki/Triplet_state" title="Triplet state">triplet ground states</a> with two unpaired electrons. In practice, such molecules distort from planar regular polygons. <a href="/wiki/Cyclobutadiene" title="Cyclobutadiene">Cyclobutadiene</a> (C<sub>4</sub>H<sub>4</sub>) with four π electrons is stable only at temperatures below 35 K and is rectangular rather than square.<sup id="cite_ref-Levine_8-2" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> <a href="/wiki/Cyclooctatetraene" title="Cyclooctatetraene">Cyclooctatetraene</a> (C<sub>8</sub>H<sub>8</sub>) with eight π electrons has a nonplanar "tub" structure. However, the dianion <span class="chemf nowrap">C<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">8</sub></span></span>H<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">2–</sup><br /><sub style="font-size:inherit;line-height:inherit;vertical-align:baseline">8</sub></span></span></span> (<a href="/wiki/Cyclooctatetraenide_anion" title="Cyclooctatetraenide anion">cyclooctatetraenide anion</a>), with ten π electrons obeys the 4<i>n</i> + 2 rule for <i>n</i> = 2 and is planar, while the 1,4-dimethyl derivative of the dication, with six π electrons, is also believed to be planar and aromatic.<sup id="cite_ref-Levine_8-3" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/Cyclononatetraene" title="Cyclononatetraene">Cyclononatetraenide anion</a> (<span class="chemf nowrap">C<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">9</sub></span></span>H<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">9</sub></span></span></span>) is the largest all-<i>cis</i> monocyclic annulene/annulenyl system that is planar and aromatic. These bond angles (140°) differ significantly from the ideal angles of 120°. Larger rings possess <i>trans</i> bonds to avoid the increased angle strain. However, 10 to 14-membered systems all experience considerable <a href="/wiki/Transannular_strain" class="mw-redirect" title="Transannular strain">transannular strain</a>. Thus, these systems are either nonaromatic or experience modest aromaticity. This changes when we get to <a href="/wiki/Cyclooctadecanonaene" title="Cyclooctadecanonaene">[18]annulene</a>, with (4×4) + 2 = 18 π electrons, which is large enough to accommodate six interior hydrogen atoms in a planar configuration (3 <i>cis</i> double bonds and 6 <i>trans</i> double bonds). Thermodynamic stabilization, NMR chemical shifts, and nearly equal bond lengths all point to considerable aromaticity for [18]annulene. </p><p>The (4n+2) rule is a consequence of the <a href="/wiki/Degenerate_energy_levels" title="Degenerate energy levels">degeneracy</a> of the π orbitals in cyclic conjugated hydrocarbon molecules. As predicted by <a href="/wiki/H%C3%BCckel_method" title="Hückel method">Hückel molecular orbital theory</a>, the lowest π orbital in such molecules is non-degenerate and the higher orbitals form degenerate pairs. Benzene's lowest π orbital is non-degenerate and can hold 2 electrons, and its next 2 π orbitals form a degenerate pair which can hold 4 electrons. Its 6 π electrons therefore form a stable closed shell in a <a href="/wiki/Regular_hexagon" class="mw-redirect" title="Regular hexagon">regular hexagonal</a> molecule.<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><sup id="cite_ref-Levine_8-4" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p><p>However for cyclobutadiene or cyclooctatrene with regular geometries, the highest molecular orbital pair is occupied by only 2 π electrons forming a less stable open shell. The molecules therefore stabilize by geometrical distortions which separate the degenerate orbital energies so that the last two electrons occupy the same orbital, but the molecule as a whole is less stable in the presence of such a distortion.<sup id="cite_ref-Levine_8-5" class="reference"><a href="#cite_note-Levine-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Heteroatoms">Heteroatoms</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=2" title="Edit section: Heteroatoms"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Hückel's rule can also be applied to molecules containing other atoms such as nitrogen or oxygen. For example, <a href="/wiki/Pyridine" title="Pyridine">pyridine</a> (C<sub>5</sub>H<sub>5</sub>N) has a ring structure similar to benzene, except that one -CH- group is replaced by a nitrogen atom with no hydrogen. There are still six π electrons and the pyridine molecule is also aromatic and known for its stability.<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> </p> <div class="mw-heading mw-heading2"><h2 id="Polycyclic_hydrocarbons">Polycyclic hydrocarbons</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=3" title="Edit section: Polycyclic hydrocarbons"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Hückel's rule is not valid for many compounds containing more than one ring. For example, <a href="/wiki/Pyrene" title="Pyrene">pyrene</a> and <a href="/wiki/Bicalicene" title="Bicalicene">trans-bicalicene</a> contain 16 <a href="/wiki/Conjugated_system" title="Conjugated system">conjugated electrons</a> (8 bonds), and <a href="/wiki/Coronene" title="Coronene">coronene</a> contains 24 conjugated electrons (12 bonds). Both of these polycyclic molecules are aromatic, even though they fail the 4<i>n</i> + 2 rule. Indeed, Hückel's rule can only be theoretically justified for monocyclic systems.<sup id="cite_ref-Roberts_5-2" class="reference"><a href="#cite_note-Roberts-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Three-dimensional_rule">Three-dimensional rule</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=4" title="Edit section: Three-dimensional rule"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <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">Main article: <a href="/wiki/Spherical_aromaticity" title="Spherical aromaticity">Spherical aromaticity</a></div> <p>In 2000, Andreas Hirsch and coworkers in <a href="/wiki/Erlangen" title="Erlangen">Erlangen</a>, <a href="/wiki/Germany" title="Germany">Germany</a>, formulated a rule to determine when a spherical compound will be aromatic. They found that closed-shell compounds were aromatic when they had 2(<i>n</i> + 1)<sup>2</sup> π-<a href="/wiki/Electrons" class="mw-redirect" title="Electrons">electrons</a>, for instance the <a href="/wiki/Buckminsterfullerene" title="Buckminsterfullerene">buckminsterfullerene</a> species C<sub>60</sub><sup>10+</sup>.<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><sup id="cite_ref-:0_16-0" class="reference"><a href="#cite_note-:0-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p><p>In 2011, Jordi Poater and Miquel Solà expanded the rule to open-shell spherical compounds, finding they were aromatic when they had 2<i>n</i><sup>2</sup> + 2<i>n</i> + 1 π-<a href="/wiki/Electrons" class="mw-redirect" title="Electrons">electrons</a>, with <a href="/wiki/Spin_(physics)" title="Spin (physics)">spin</a> S = (n + 1/2) - corresponding to a half-filled last occupied energy level with the same spin. For instance C<sub>60</sub><sup>1–</sup> is also observed to be aromatic with a spin of 11/2.<sup id="cite_ref-:0_16-1" class="reference"><a href="#cite_note-:0-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Baird%27s_rule" title="Baird's rule">Baird's rule</a> (for triplet states)</li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=H%C3%BCckel%27s_rule&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <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"> <div class="mw-references-wrap mw-references-columns"><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"> <ul><li><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 a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .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="CITEREFHückel1931" class="citation journal cs1"><a href="/wiki/Erich_H%C3%BCckel" title="Erich Hückel">Hückel, Erich</a> (1931). "Quantentheoretische Beiträge zum Benzolproblem I. Die Elektronenkonfiguration des Benzols und verwandter Verbindungen". <i><a href="/wiki/Z._Phys." class="mw-redirect" title="Z. Phys.">Z. Phys.</a></i> <b>70</b> (<span class="nowrap">3–</span>4): <span class="nowrap">204–</span>86. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1931ZPhy...70..204H">1931ZPhy...70..204H</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2FBF01339530">10.1007/BF01339530</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:186218131">186218131</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Z.+Phys.&rft.atitle=Quantentheoretische+Beitr%C3%A4ge+zum+Benzolproblem+I.+Die+Elektronenkonfiguration+des+Benzols+und+verwandter+Verbindungen&rft.volume=70&rft.issue=%3Cspan+class%3D%22nowrap%22%3E3%E2%80%93%3C%2Fspan%3E4&rft.pages=%3Cspan+class%3D%22nowrap%22%3E204-%3C%2Fspan%3E86&rft.date=1931&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A186218131%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1007%2FBF01339530&rft_id=info%3Abibcode%2F1931ZPhy...70..204H&rft.aulast=H%C3%BCckel&rft.aufirst=Erich&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFHückel1931" class="citation journal cs1"><a href="/wiki/Erich_H%C3%BCckel" title="Erich Hückel">Hückel, Erich</a> (1931). "Quanstentheoretische Beiträge zum Benzolproblem II. Quantentheorie der induzierten Polaritäten". <i>Z. Phys</i>. <b>72</b> (<span class="nowrap">5–</span>6): <span class="nowrap">310–</span>37. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1931ZPhy...72..310H">1931ZPhy...72..310H</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2FBF01341953">10.1007/BF01341953</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Z.+Phys.&rft.atitle=Quanstentheoretische+Beitr%C3%A4ge+zum+Benzolproblem+II.+Quantentheorie+der+induzierten+Polarit%C3%A4ten&rft.volume=72&rft.issue=%3Cspan+class%3D%22nowrap%22%3E5%E2%80%93%3C%2Fspan%3E6&rft.pages=%3Cspan+class%3D%22nowrap%22%3E310-%3C%2Fspan%3E37&rft.date=1931&rft_id=info%3Adoi%2F10.1007%2FBF01341953&rft_id=info%3Abibcode%2F1931ZPhy...72..310H&rft.aulast=H%C3%BCckel&rft.aufirst=Erich&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFHückel1932" class="citation journal cs1"><a href="/wiki/Erich_H%C3%BCckel" title="Erich Hückel">Hückel, Erich</a> (1932). "Quantentheoretische Beiträge zum Problem der aromatischen und ungesättigten Verbindungen. III". <i>Z. Phys</i>. <b>76</b> (<span class="nowrap">9–</span>10): <span class="nowrap">628–</span>48. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1932ZPhy...76..628H">1932ZPhy...76..628H</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2FBF01341936">10.1007/BF01341936</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:121787219">121787219</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Z.+Phys.&rft.atitle=Quantentheoretische+Beitr%C3%A4ge+zum+Problem+der+aromatischen+und+unges%C3%A4ttigten+Verbindungen.+III&rft.volume=76&rft.issue=%3Cspan+class%3D%22nowrap%22%3E9%E2%80%93%3C%2Fspan%3E10&rft.pages=%3Cspan+class%3D%22nowrap%22%3E628-%3C%2Fspan%3E48&rft.date=1932&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A121787219%23id-name%3DS2CID&rft_id=info%3Adoi%2F10.1007%2FBF01341936&rft_id=info%3Abibcode%2F1932ZPhy...76..628H&rft.aulast=H%C3%BCckel&rft.aufirst=Erich&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></li></ul> </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"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFHückel1938" class="citation book cs1"><a href="/wiki/Erich_H%C3%BCckel" title="Erich Hückel">Hückel, E.</a> (1938). <i>Grundzüge der Theorie ungesättiger und aromatischer Verbindungen</i>. Berlin: Verlag Chem. pp. <span class="nowrap">77–</span>85.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Grundz%C3%BCge+der+Theorie+unges%C3%A4ttiger+und+aromatischer+Verbindungen&rft.place=Berlin&rft.pages=%3Cspan+class%3D%22nowrap%22%3E77-%3C%2Fspan%3E85&rft.pub=Verlag+Chem&rft.date=1938&rft.aulast=H%C3%BCckel&rft.aufirst=E.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFDoeringDetert1951" class="citation journal cs1">Doering, W. VON E.; Detert, Francis L. (1951-02-01). "Cycloheptatrienylium Oxide". <i>Journal of the American Chemical Society</i>. <b>73</b> (2): <span class="nowrap">876–</span>877. <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%2Fja01146a537">10.1021/ja01146a537</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0002-7863">0002-7863</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Journal+of+the+American+Chemical+Society&rft.atitle=Cycloheptatrienylium+Oxide&rft.volume=73&rft.issue=2&rft.pages=%3Cspan+class%3D%22nowrap%22%3E876-%3C%2Fspan%3E877&rft.date=1951-02-01&rft_id=info%3Adoi%2F10.1021%2Fja01146a537&rft.issn=0002-7863&rft.aulast=Doering&rft.aufirst=W.+VON+E.&rft.au=Detert%2C+Francis+L.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" 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 id="CITEREFDoering1951" class="citation cs2">Doering, W. v. E. (September 1951), <i>Abstracts of the American Chemical Society Meeting, New York</i>, p. 24M</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Abstracts+of+the+American+Chemical+Society+Meeting%2C+New+York&rft.pages=24M&rft.date=1951-09&rft.aulast=Doering&rft.aufirst=W.+v.+E.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-Roberts-5"><span class="mw-cite-backlink">^ <a href="#cite_ref-Roberts_5-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Roberts_5-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Roberts_5-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFRobertsStreitwieserRegan1952" class="citation journal cs1">Roberts, John D.; <a href="/wiki/Andrew_Streitwieser" title="Andrew Streitwieser">Streitwieser, Andrew Jr.</a>; Regan, Clare M. (1952). "Small-Ring Compounds. X. Molecular Orbital Calculations of Properties of Some Small-Ring Hydrocarbons and Free Radicals". <i>J. Am. Chem. Soc</i>. <b>74</b> (18): <span class="nowrap">4579–</span>82. <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%2Fja01138a038">10.1021/ja01138a038</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=J.+Am.+Chem.+Soc.&rft.atitle=Small-Ring+Compounds.+X.+Molecular+Orbital+Calculations+of+Properties+of+Some+Small-Ring+Hydrocarbons+and+Free+Radicals&rft.volume=74&rft.issue=18&rft.pages=%3Cspan+class%3D%22nowrap%22%3E4579-%3C%2Fspan%3E82&rft.date=1952&rft_id=info%3Adoi%2F10.1021%2Fja01138a038&rft.aulast=Roberts&rft.aufirst=John+D.&rft.au=Streitwieser%2C+Andrew+Jr.&rft.au=Regan%2C+Clare+M.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" 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="CITEREFMarch1985" class="citation book cs1"><a href="/wiki/Jerry_March" title="Jerry March">March, Jerry</a> (1985). <a rel="nofollow" class="external text" href="https://www.google.co.in/books/edition/_/ZKqWAQAACAAJ?hl=en"><i>Advanced Organic Chemistry: Reactions, Mechanisms, and Structure</i></a> (3rd ed.). New York: Wiley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780471854722" title="Special:BookSources/9780471854722"><bdi>9780471854722</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/642506595">642506595</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Advanced+Organic+Chemistry%3A+Reactions%2C+Mechanisms%2C+and+Structure&rft.place=New+York&rft.edition=3rd&rft.pub=Wiley&rft.date=1985&rft_id=info%3Aoclcnum%2F642506595&rft.isbn=9780471854722&rft.aulast=March&rft.aufirst=Jerry&rft_id=https%3A%2F%2Fwww.google.co.in%2Fbooks%2Fedition%2F_%2FZKqWAQAACAAJ%3Fhl%3Den&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" 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="CITEREFAyub2017" class="citation web cs1">Ayub, Rabia (2017). <a rel="nofollow" class="external text" href="https://www.diva-portal.org/smash/get/diva2:1152985/FULLTEXT01.pdf">"Excited State Aromaticity and Antiaromaticity. Fundamental Studies and Applications"</a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/Uppsala_University" title="Uppsala University">Uppsala University</a>. p. 15<span class="reference-accessdate">. Retrieved <span class="nowrap">26 January</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Excited+State+Aromaticity+and+Antiaromaticity.+Fundamental+Studies+and+Applications.&rft.pages=15&rft.pub=Uppsala+University&rft.date=2017&rft.aulast=Ayub&rft.aufirst=Rabia&rft_id=https%3A%2F%2Fwww.diva-portal.org%2Fsmash%2Fget%2Fdiva2%3A1152985%2FFULLTEXT01.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-Levine-8"><span class="mw-cite-backlink">^ <a href="#cite_ref-Levine_8-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Levine_8-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Levine_8-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-Levine_8-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-Levine_8-4"><sup><i><b>e</b></i></sup></a> <a href="#cite_ref-Levine_8-5"><sup><i><b>f</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFLevine1991" class="citation book cs1"><a href="/wiki/Ira_N._Levine" title="Ira N. Levine">Levine, I. N.</a> (1991). <i>Quantum chemistry</i> (4th ed.). Prentice-Hall. pp. <span class="nowrap">558–</span>560. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-205-12770-2" title="Special:BookSources/978-0-205-12770-2"><bdi>978-0-205-12770-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Quantum+chemistry&rft.pages=%3Cspan+class%3D%22nowrap%22%3E558-%3C%2Fspan%3E560&rft.edition=4th&rft.pub=Prentice-Hall&rft.date=1991&rft.isbn=978-0-205-12770-2&rft.aulast=Levine&rft.aufirst=I.+N.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFMarch1985" class="citation book cs1"><a href="/wiki/Jerry_March" title="Jerry March">March, Jerry</a> (1985). <a rel="nofollow" class="external text" href="https://www.google.co.in/books/edition/_/ZKqWAQAACAAJ?hl=en"><i>Advanced Organic Chemistry: Reactions, Mechanisms, and Structure</i></a> (3rd ed.). New York: Wiley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9780471854722" title="Special:BookSources/9780471854722"><bdi>9780471854722</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/642506595">642506595</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Advanced+Organic+Chemistry%3A+Reactions%2C+Mechanisms%2C+and+Structure&rft.place=New+York&rft.edition=3rd&rft.pub=Wiley&rft.date=1985&rft_id=info%3Aoclcnum%2F642506595&rft.isbn=9780471854722&rft.aulast=March&rft.aufirst=Jerry&rft_id=https%3A%2F%2Fwww.google.co.in%2Fbooks%2Fedition%2F_%2FZKqWAQAACAAJ%3Fhl%3Den&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" 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="CITEREFBreslowGroves1970" class="citation journal cs1">Breslow, Ronald; Groves, John T. (1970). "Cyclopropenyl cation. Synthesis and characterization". <i><a href="/wiki/J._Am._Chem._Soc." class="mw-redirect" title="J. Am. Chem. Soc.">J. Am. Chem. Soc.</a></i> <b>92</b> (4): <span class="nowrap">984–</span>987. <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%2Fja00707a040">10.1021/ja00707a040</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=J.+Am.+Chem.+Soc.&rft.atitle=Cyclopropenyl+cation.+Synthesis+and+characterization&rft.volume=92&rft.issue=4&rft.pages=%3Cspan+class%3D%22nowrap%22%3E984-%3C%2Fspan%3E987&rft.date=1970&rft_id=info%3Adoi%2F10.1021%2Fja00707a040&rft.aulast=Breslow&rft.aufirst=Ronald&rft.au=Groves%2C+John+T.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" 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="CITEREFWrackmeyer2016" class="citation journal cs1">Wrackmeyer, B. (2016). "A Cyclotriborane Dianion and the Triboron Cation: "Light Ends" of the Hückel Rule". <i><a href="/wiki/Angew._Chem._Int._Ed." class="mw-redirect" title="Angew. Chem. Int. Ed.">Angew. Chem. Int. Ed.</a></i> <b>55</b> (6): <span class="nowrap">1962–</span>64. <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%2Fanie.201510689">10.1002/anie.201510689</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/26765534">26765534</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Angew.+Chem.+Int.+Ed.&rft.atitle=A+Cyclotriborane+Dianion+and+the+Triboron+Cation%3A+%22Light+Ends%22+of+the+H%C3%BCckel+Rule&rft.volume=55&rft.issue=6&rft.pages=%3Cspan+class%3D%22nowrap%22%3E1962-%3C%2Fspan%3E64&rft.date=2016&rft_id=info%3Adoi%2F10.1002%2Fanie.201510689&rft_id=info%3Apmid%2F26765534&rft.aulast=Wrackmeyer&rft.aufirst=B.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFKupferBraunschweigRadacki2015" class="citation journal cs1">Kupfer, T.; Braunschweig, H.; Radacki, K. (2015). "The Triboracyclopropenyl Dianion: The Lightest Possible Main-Group-Element Hückel π Aromatic". <i><a href="/wiki/Angew._Chem._Int._Ed." class="mw-redirect" title="Angew. Chem. Int. Ed.">Angew. Chem. Int. Ed.</a></i> <b>54</b> (50): <span class="nowrap">15084–</span>15088. <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%2Fanie.201508670">10.1002/anie.201508670</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/26530854">26530854</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Angew.+Chem.+Int.+Ed.&rft.atitle=The+Triboracyclopropenyl+Dianion%3A+The+Lightest+Possible+Main-Group-Element+H%C3%BCckel+%CF%80+Aromatic.&rft.volume=54&rft.issue=50&rft.pages=%3Cspan+class%3D%22nowrap%22%3E15084-%3C%2Fspan%3E15088&rft.date=2015&rft_id=info%3Adoi%2F10.1002%2Fanie.201508670&rft_id=info%3Apmid%2F26530854&rft.aulast=Kupfer&rft.aufirst=T.&rft.au=Braunschweig%2C+H.&rft.au=Radacki%2C+K.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFAtkinsde_Paula2002" class="citation book cs1">Atkins, Peter; de Paula, Julio (2002). <i>Physical Chemistry</i> (7th ed.). W. H. Freeman. p. 437-8. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-7167-3539-3" title="Special:BookSources/0-7167-3539-3"><bdi>0-7167-3539-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Physical+Chemistry&rft.pages=437-8&rft.edition=7th&rft.pub=W.+H.+Freeman&rft.date=2002&rft.isbn=0-7167-3539-3&rft.aulast=Atkins&rft.aufirst=Peter&rft.au=de+Paula%2C+Julio&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</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://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(McMurry)/15%3A_Benzene_and_Aromaticity/15.05%3A_Aromatic_Heterocycles-_Pyridine_and_Pyrrole">"Aromatic Heterocycles- Pyridine and Pyrrole"</a>. <i>Chemistry Libre Texts</i>. 3 May 2015. p. 15.5<span class="reference-accessdate">. Retrieved <span class="nowrap">1 March</span> 2022</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Chemistry+Libre+Texts&rft.atitle=Aromatic+Heterocycles-+Pyridine+and+Pyrrole&rft.pages=15.5&rft.date=2015-05-03&rft_id=https%3A%2F%2Fchem.libretexts.org%2FBookshelves%2FOrganic_Chemistry%2FOrganic_Chemistry_%28McMurry%29%2F15%253A_Benzene_and_Aromaticity%2F15.05%253A_Aromatic_Heterocycles-_Pyridine_and_Pyrrole&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span></span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFHirschChenJiao2000" class="citation journal cs1">Hirsch, Andreas; Chen, Zhongfang; Jiao, Haijun (2000). "Spherical Aromaticity in <i>I</i><sub>h</sub> Symmetrical Fullerenes: The 2(<i>N</i>+1)<sup>2</sup> Rule". <i>Angew. Chem. Int. Ed. Engl</i>. <b>39</b> (21): <span class="nowrap">3915–</span>17. <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%2F1521-3773%2820001103%2939%3A21%3C3915%3A%3AAID-ANIE3915%3E3.0.CO%3B2-O">10.1002/1521-3773(20001103)39:21<3915::AID-ANIE3915>3.0.CO;2-O</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/29711706">29711706</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Angew.+Chem.+Int.+Ed.+Engl.&rft.atitle=Spherical+Aromaticity+in+I%3Csub%3Eh%3C%2Fsub%3E+Symmetrical+Fullerenes%3A+The+2%28N%2B1%29%3Csup%3E2%3C%2Fsup%3E+Rule&rft.volume=39&rft.issue=21&rft.pages=%3Cspan+class%3D%22nowrap%22%3E3915-%3C%2Fspan%3E17&rft.date=2000&rft_id=info%3Adoi%2F10.1002%2F1521-3773%2820001103%2939%3A21%3C3915%3A%3AAID-ANIE3915%3E3.0.CO%3B2-O&rft_id=info%3Apmid%2F29711706&rft.aulast=Hirsch&rft.aufirst=Andreas&rft.au=Chen%2C+Zhongfang&rft.au=Jiao%2C+Haijun&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span>.</span> </li> <li id="cite_note-:0-16"><span class="mw-cite-backlink">^ <a href="#cite_ref-:0_16-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:0_16-1"><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="CITEREFPoaterSolà2011" class="citation journal cs1">Poater, Jordi; Solà, Miquel (2011). "Open-shell spherical aromaticity: the 2<i>N</i><sup>2</sup> + 2<i>N</i> + 1 (with <i>S</i> = <i>N</i> + ½) rule". <i><a href="/wiki/Chem._Comm." class="mw-redirect" title="Chem. Comm.">Chem. Comm.</a></i> <b>47</b> (42): <span class="nowrap">11647–</span>11649. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1039%2FC1CC14958J">10.1039/C1CC14958J</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/21952479">21952479</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Chem.+Comm.&rft.atitle=Open-shell+spherical+aromaticity%3A+the+2N%3Csup%3E2%3C%2Fsup%3E+%2B+2N+%2B+1+%28with+S+%3D+N+%2B+%C2%BD%29+rule&rft.volume=47&rft.issue=42&rft.pages=%3Cspan+class%3D%22nowrap%22%3E11647-%3C%2Fspan%3E11649&rft.date=2011&rft_id=info%3Adoi%2F10.1039%2FC1CC14958J&rft_id=info%3Apmid%2F21952479&rft.aulast=Poater&rft.aufirst=Jordi&rft.au=Sol%C3%A0%2C+Miquel&rfr_id=info%3Asid%2Fen.wikipedia.org%3AH%C3%BCckel%27s+rule" class="Z3988"></span>.</span> </li> </ol></div></div> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}</style></div><div role="navigation" class="navbox" aria-labelledby="Chemical_bonds164" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="3"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Chemical_bonds" title="Template:Chemical bonds"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Chemical_bonds" title="Template talk:Chemical bonds"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Chemical_bonds" title="Special:EditPage/Template:Chemical bonds"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Chemical_bonds164" style="font-size:114%;margin:0 4em"><a href="/wiki/Chemical_bond" title="Chemical bond">Chemical bonds</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Intramolecular_force" title="Intramolecular force">Intramolecular</a><br />(strong)</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Covalent_bond" title="Covalent bond">Covalent</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Electron_deficiency" title="Electron deficiency">Electron deficiency</a> <ul><li><a href="/wiki/Three-center_two-electron_bond" title="Three-center two-electron bond">3c–2e</a></li> <li><a href="/wiki/Four-center_two-electron_bond" title="Four-center two-electron bond">4c–2e</a></li> <li><a href="/wiki/Eight-center_two-electron_bond" class="mw-redirect" title="Eight-center two-electron bond">8c–2e</a></li></ul></li> <li><a href="/wiki/Hypervalent_molecule" title="Hypervalent molecule">Hypervalence</a> <ul><li><a href="/wiki/Three-center_four-electron_bond" title="Three-center four-electron bond">3c–4e</a></li></ul></li> <li><a href="/wiki/Agostic_interaction" title="Agostic interaction">Agostic</a></li> <li><a href="/wiki/Bent_bond" title="Bent bond">Bent</a></li> <li><a href="/wiki/Coordinate_covalent_bond" title="Coordinate covalent bond">Coordinate (dipolar)</a></li> <li><a href="/wiki/Pi_backbonding" title="Pi backbonding">Pi backbond</a></li> <li><a href="/wiki/Metal%E2%80%93ligand_multiple_bond" title="Metal–ligand multiple bond">Metal–ligand multiple bond</a></li> <li><a href="/wiki/Charge-shift_bond" title="Charge-shift bond">Charge-shift</a></li> <li><a href="/wiki/Hapticity" title="Hapticity">Hapticity</a></li> <li><a href="/wiki/Conjugated_system" title="Conjugated system">Conjugation</a></li> <li><a href="/wiki/Hyperconjugation" title="Hyperconjugation">Hyperconjugation</a></li> <li><a href="/wiki/Aromaticity" title="Aromaticity">Aromaticity</a> <ul><li><a href="/wiki/Homoaromaticity" title="Homoaromaticity">homo</a></li> <li><a href="/wiki/Bicycloaromaticity" title="Bicycloaromaticity">bicyclo</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Metallic_bonding" title="Metallic bonding">Metallic</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Metal_aromaticity" title="Metal aromaticity">Metal aromaticity</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Ionic_bonding" title="Ionic bonding">Ionic</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li class="mw-empty-elt"></li></ul> </div></td></tr></tbody></table><div></div></td><td class="noviewer navbox-image" rowspan="4" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/wiki/File:Ligatio-covalens.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/21/Ligatio-covalens.svg/200px-Ligatio-covalens.svg.png" decoding="async" width="200" height="89" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/21/Ligatio-covalens.svg/300px-Ligatio-covalens.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/21/Ligatio-covalens.svg/400px-Ligatio-covalens.svg.png 2x" data-file-width="597" data-file-height="265" /></a></span><br /><span typeof="mw:File"><a href="/wiki/File:Chemfm_carbon_monoxide_3_1.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/77/Chemfm_carbon_monoxide_3_1.svg/200px-Chemfm_carbon_monoxide_3_1.svg.png" decoding="async" width="200" height="113" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/77/Chemfm_carbon_monoxide_3_1.svg/300px-Chemfm_carbon_monoxide_3_1.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/77/Chemfm_carbon_monoxide_3_1.svg/400px-Chemfm_carbon_monoxide_3_1.svg.png 2x" data-file-width="99" data-file-height="56" /></a></span><br /><span typeof="mw:File"><a href="/wiki/File:Pi-Bond.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Pi-Bond.svg/250px-Pi-Bond.svg.png" decoding="async" width="200" height="113" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/70/Pi-Bond.svg/330px-Pi-Bond.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/70/Pi-Bond.svg/500px-Pi-Bond.svg.png 2x" data-file-width="1920" data-file-height="1080" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Intermolecular_force" title="Intermolecular force">Intermolecular</a><br />(weak)</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Van_der_Waals_force" title="Van der Waals force">Van der Waals<br />forces</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/London_dispersion_force" title="London dispersion force">London dispersion</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Hydrogen_bond" title="Hydrogen bond">Hydrogen</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Low-barrier_hydrogen_bond" title="Low-barrier hydrogen bond">Low-barrier</a></li> <li><a href="/wiki/Resonance-assisted_hydrogen_bond" class="mw-redirect" title="Resonance-assisted hydrogen bond">Resonance-assisted</a></li> <li><a href="/wiki/Symmetric_hydrogen_bond" title="Symmetric hydrogen bond">Symmetric</a></li> <li><a href="/wiki/Dihydrogen_bond" title="Dihydrogen bond">Dihydrogen bonds</a></li> <li><a href="/wiki/C%E2%80%93H%C2%B7%C2%B7%C2%B7O_interaction" title="C–H···O interaction">C–H···O interaction</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Non-covalent_interactions" class="mw-redirect" title="Non-covalent interactions">Noncovalent</a><br />other</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Mechanically_interlocked_molecular_architectures" title="Mechanically interlocked molecular architectures">Mechanical</a></li> <li><a href="/wiki/Halogen_bond" title="Halogen bond">Halogen</a></li> <li><a href="/wiki/Chalcogen_bond" title="Chalcogen bond">Chalcogen</a></li> <li><a href="/wiki/Metallophilic_interaction" title="Metallophilic interaction">Metallophilic</a> (<a href="/wiki/Aurophilicity" title="Aurophilicity">aurophilic</a>)</li> <li><a href="/wiki/Intercalation_(chemistry)" title="Intercalation (chemistry)">Intercalation</a></li> <li><a href="/wiki/Stacking_(chemistry)" title="Stacking (chemistry)">Stacking</a></li> <li><a href="/wiki/Cation%E2%80%93pi_interaction" class="mw-redirect" title="Cation–pi interaction">Cation–pi</a></li> <li><a href="/wiki/Cation%E2%80%93pi_interaction#Anion–π_interaction" class="mw-redirect" title="Cation–pi interaction">Anion–pi</a></li> <li><a href="/wiki/Salt_bridge_(protein_and_supramolecular)" title="Salt bridge (protein and supramolecular)">Salt bridge</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Bond_cleavage" title="Bond cleavage">Bond cleavage</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Heterolysis_(chemistry)" title="Heterolysis (chemistry)">Heterolysis</a></li> <li><a href="/wiki/Homolysis_(chemistry)" title="Homolysis (chemistry)">Homolysis</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Electron_counting" title="Electron counting">Electron counting</a> rules</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Aromaticity" title="Aromaticity">Aromaticity</a> <ul><li><a class="mw-selflink selflink">Hückel's rule</a></li> <li><a href="/wiki/Baird%27s_rule" title="Baird's rule">Baird's rule</a></li> <li><a href="/wiki/M%C3%B6bius_aromaticity" title="Möbius aromaticity">Möbius</a></li> <li><a href="/wiki/Spherical_aromaticity" title="Spherical aromaticity">spherical</a></li></ul></li> <li><a href="/wiki/Polyhedral_skeletal_electron_pair_theory" title="Polyhedral skeletal electron pair theory">Polyhedral skeletal electron pair theory</a></li> <li><a href="/wiki/Jemmis_mno_rules" title="Jemmis mno rules">Jemmis mno rules</a></li></ul> </div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?useformat=desktop&type=1x1&usesul3=0" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Hückel%27s_rule&oldid=1276109541">https://en.wikipedia.org/w/index.php?title=Hückel%27s_rule&oldid=1276109541</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Categories</a>: <ul><li><a href="/wiki/Category:Physical_organic_chemistry" title="Category:Physical organic chemistry">Physical organic chemistry</a></li><li><a href="/wiki/Category:Rules_of_thumb" title="Category:Rules of thumb">Rules of thumb</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_matches_Wikidata" title="Category:Short description matches Wikidata">Short description matches Wikidata</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 16 February 2025, at 22:54<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. By using this site, you agree to the <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Terms_of_Use" class="extiw" title="foundation:Special:MyLanguage/Policy:Terms of Use">Terms of Use</a> and <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy" class="extiw" title="foundation:Special:MyLanguage/Policy:Privacy policy">Privacy Policy</a>. Wikipedia® is a registered trademark of the <a rel="nofollow" class="external text" href="https://wikimediafoundation.org/">Wikimedia Foundation, Inc.</a>, a non-profit organization.</li> </ul> <ul id="footer-places"> <li id="footer-places-privacy"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy">Privacy policy</a></li> <li id="footer-places-about"><a href="/wiki/Wikipedia:About">About Wikipedia</a></li> <li id="footer-places-disclaimers"><a href="/wiki/Wikipedia:General_disclaimer">Disclaimers</a></li> <li id="footer-places-contact"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us">Contact Wikipedia</a></li> <li id="footer-places-wm-codeofconduct"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Universal_Code_of_Conduct">Code of Conduct</a></li> <li id="footer-places-developers"><a href="https://developer.wikimedia.org">Developers</a></li> <li id="footer-places-statslink"><a href="https://stats.wikimedia.org/#/en.wikipedia.org">Statistics</a></li> <li id="footer-places-cookiestatement"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Cookie_statement">Cookie statement</a></li> <li id="footer-places-mobileview"><a href="//en.m.wikipedia.org/w/index.php?title=H%C3%BCckel%27s_rule&mobileaction=toggle_view_mobile" class="noprint stopMobileRedirectToggle">Mobile view</a></li> </ul> <ul id="footer-icons" class="noprint"> <li id="footer-copyrightico"><a href="https://www.wikimedia.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><picture><source media="(min-width: 500px)" srcset="/static/images/footer/wikimedia-button.svg" width="84" height="29"><img src="/static/images/footer/wikimedia.svg" width="25" height="25" alt="Wikimedia Foundation" lang="en" loading="lazy"></picture></a></li> <li id="footer-poweredbyico"><a href="https://www.mediawiki.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><picture><source media="(min-width: 500px)" srcset="/w/resources/assets/poweredby_mediawiki.svg" width="88" height="31"><img src="/w/resources/assets/mediawiki_compact.svg" alt="Powered by MediaWiki" lang="en" width="25" height="25" loading="lazy"></picture></a></li> </ul> </footer> </div> </div> </div> <div class="vector-header-container vector-sticky-header-container"> <div id="vector-sticky-header" class="vector-sticky-header"> <div class="vector-sticky-header-start"> <div class="vector-sticky-header-icon-start vector-button-flush-left vector-button-flush-right" aria-hidden="true"> <button class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-sticky-header-search-toggle" tabindex="-1" data-event-name="ui.vector-sticky-search-form.icon"><span class="vector-icon mw-ui-icon-search mw-ui-icon-wikimedia-search"></span> <span>Search</span> </button> </div> <div role="search" class="vector-search-box-vue vector-search-box-show-thumbnail vector-search-box"> <div class="vector-typeahead-search-container"> <div class="cdx-typeahead-search cdx-typeahead-search--show-thumbnail"> <form action="/w/index.php" id="vector-sticky-search-form" class="cdx-search-input cdx-search-input--has-end-button"> <div class="cdx-search-input__input-wrapper" data-search-loc="header-moved"> <div class="cdx-text-input cdx-text-input--has-start-icon"> <input class="cdx-text-input__input" type="search" name="search" placeholder="Search Wikipedia"> <span class="cdx-text-input__icon cdx-text-input__start-icon"></span> </div> <input type="hidden" name="title" value="Special:Search"> </div> <button class="cdx-button cdx-search-input__end-button">Search</button> </form> </div> </div> </div> <div class="vector-sticky-header-context-bar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-sticky-header-toc" class="vector-dropdown mw-portlet mw-portlet-sticky-header-toc vector-sticky-header-toc vector-button-flush-left" > <input type="checkbox" id="vector-sticky-header-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-sticky-header-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-sticky-header-toc-label" for="vector-sticky-header-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-sticky-header-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <div class="vector-sticky-header-context-bar-primary" aria-hidden="true" ><span class="mw-page-title-main">Hückel's rule</span></div> </div> </div> <div class="vector-sticky-header-end" aria-hidden="true"> <div class="vector-sticky-header-icons"> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-talk-sticky-header" tabindex="-1" data-event-name="talk-sticky-header"><span class="vector-icon mw-ui-icon-speechBubbles mw-ui-icon-wikimedia-speechBubbles"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-subject-sticky-header" tabindex="-1" data-event-name="subject-sticky-header"><span class="vector-icon mw-ui-icon-article mw-ui-icon-wikimedia-article"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-history-sticky-header" tabindex="-1" data-event-name="history-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-history mw-ui-icon-wikimedia-wikimedia-history"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only mw-watchlink" id="ca-watchstar-sticky-header" tabindex="-1" data-event-name="watch-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-star mw-ui-icon-wikimedia-wikimedia-star"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-edit-sticky-header" tabindex="-1" data-event-name="wikitext-edit-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-wikiText mw-ui-icon-wikimedia-wikimedia-wikiText"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-ve-edit-sticky-header" tabindex="-1" data-event-name="ve-edit-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-edit mw-ui-icon-wikimedia-wikimedia-edit"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-viewsource-sticky-header" tabindex="-1" data-event-name="ve-edit-protected-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-editLock mw-ui-icon-wikimedia-wikimedia-editLock"></span> <span></span> </a> </div> <div class="vector-sticky-header-buttons"> <button class="cdx-button cdx-button--weight-quiet mw-interlanguage-selector" id="p-lang-btn-sticky-header" tabindex="-1" data-event-name="ui.dropdown-p-lang-btn-sticky-header"><span class="vector-icon mw-ui-icon-wikimedia-language mw-ui-icon-wikimedia-wikimedia-language"></span> <span>21 languages</span> </button> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive" id="ca-addsection-sticky-header" tabindex="-1" data-event-name="addsection-sticky-header"><span class="vector-icon mw-ui-icon-speechBubbleAdd-progressive mw-ui-icon-wikimedia-speechBubbleAdd-progressive"></span> <span>Add topic</span> </a> </div> <div class="vector-sticky-header-icon-end"> <div class="vector-user-links"> </div> </div> </div> </div> </div> <div class="mw-portlet mw-portlet-dock-bottom emptyPortlet" id="p-dock-bottom"> <ul> </ul> </div> <script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.eqiad.main-56b45f5767-qj26m","wgBackendResponseTime":153,"wgPageParseReport":{"limitreport":{"cputime":"0.530","walltime":"0.661","ppvisitednodes":{"value":2815,"limit":1000000},"postexpandincludesize":{"value":106037,"limit":2097152},"templateargumentsize":{"value":5070,"limit":2097152},"expansiondepth":{"value":16,"limit":100},"expensivefunctioncount":{"value":2,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":75824,"limit":5000000},"entityaccesscount":{"value":1,"limit":400},"timingprofile":["100.00% 582.482 1 -total"," 45.35% 264.156 1 Template:Reflist"," 28.41% 165.458 10 Template:Cite_journal"," 19.19% 111.761 1 Template:Chemical_bonds"," 18.89% 110.049 3 Template:Navbox"," 17.46% 101.690 1 Template:Short_description"," 8.58% 49.961 2 Template:Pagetype"," 7.05% 41.078 6 Template:Chem"," 6.23% 36.265 6 Template:Chem/link"," 6.08% 35.426 3 Template:Main_other"]},"scribunto":{"limitreport-timeusage":{"value":"0.340","limit":"10.000"},"limitreport-memusage":{"value":5622724,"limit":52428800}},"cachereport":{"origin":"mw-web.eqiad.main-65bf7dbd64-4j77m","timestamp":"20250325193925","ttl":2592000,"transientcontent":false}}});});</script> <script type="application/ld+json">{"@context":"https:\/\/schema.org","@type":"Article","name":"H\u00fcckel's rule","url":"https:\/\/en.wikipedia.org\/wiki\/H%C3%BCckel%27s_rule","sameAs":"http:\/\/www.wikidata.org\/entity\/Q534307","mainEntity":"http:\/\/www.wikidata.org\/entity\/Q534307","author":{"@type":"Organization","name":"Contributors to Wikimedia projects"},"publisher":{"@type":"Organization","name":"Wikimedia Foundation, Inc.","logo":{"@type":"ImageObject","url":"https:\/\/www.wikimedia.org\/static\/images\/wmf-hor-googpub.png"}},"datePublished":"2004-07-28T02:02:48Z","dateModified":"2025-02-16T22:54:40Z","image":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/d\/da\/Benzol.svg","headline":"method of determining aromaticity in organic molecules"}</script> </body> </html>