{"id":1887,"date":"2010-04-06T12:36:51","date_gmt":"2010-04-06T11:36:51","guid":{"rendered":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887"},"modified":"2023-09-16T19:41:48","modified_gmt":"2023-09-16T18:41:48","slug":"the-conformation-of-12-difluoroethane","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","title":{"rendered":"The conformation of 1,2-difluoroethane"},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"1887\">\n<p>Here I offer another spin-off from writing a lecture course on conformational analysis. This is the famous example of why <strong>1,2-difluoroethane<\/strong> adopts a <em>gauche<\/em> rather than <em>antiperiplanar<\/em> conformation.<br \/>\n<div id=\"attachment_1888\" style=\"width: 410px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1888\" class=\"size-full wp-image-1888\" title=\"difluoroethane\" alt=\"\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg\" width=\"400\" height=\"158\" srcset=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg 952w, https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane-300x118.jpg 300w\" sizes=\"auto, (max-width: 400px) 100vw, 400px\" \/><\/a><p id=\"caption-attachment-1888\" class=\"wp-caption-text\">The gauche and antiperiplanar conformations of 1,2-difluoroethane<\/p><\/div><\/p>\n<p>One major contribution to the greater stability of the gauche is the stereoelectronic interactions, and this is best probed using the NBO (Natural Bond Orbital) approach of Weinhold (DOI: <a href=\"http:\/\/dx.doi.org\/10.1021\/ja00501a009\">10.1021\/ja00501a009<\/a>). The process is approximately described as first reducing the wavefunction down to a set of orbitals which have been localized (using appropriate algorithms) down to two or one centres (corresponding to two-centre covalent bonds, or one-centre electron lone pairs). Perturbation theory is then used to evaluate the interaction energy between any filled and any empty combination. For the molecule above,<strong> six<\/strong> such combinations are inspected, involving any one of the six filled C-H or C-F \u03c3-orbitals, and the best-overlapping \u03c3* orbital which turns out to be located on the C-H or C-F bond anti-periplanar to the filled orbital.<\/p>\n<table border=\"0\">\n<tbody>\n<tr>\n<td>\n<div id=\"attachment_1891\" style=\"width: 210px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1891\" class=\"size-full wp-image-1891\" title=\"fluoroethane1\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2010\/04\/11.jvxl;isosurface  &quot;&quot; color yellow green translucent;isosurface append wp-content\/uploads\/2010\/04\/18.jvxl translucent;set fontscaling TRUE; font label 18;select atomno=3;color black;label %A C-H \u03c3 orbital;');\" alt=\"\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/fluoroethane1.jpg\" width=\"200\" height=\"207\" \/><p id=\"caption-attachment-1891\" class=\"wp-caption-text\">Filled C-H NBO orbital. Click for 3D to superimpose empty C-F anti bonding orbital.<\/p><\/div>\n<\/td>\n<td>\n<div id=\"attachment_1892\" style=\"width: 210px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-1892\" class=\"size-full wp-image-1892\" title=\"fluoroethane2\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2010\/04\/18.jvxl;isosurface &quot;&quot; translucent;set fontscaling TRUE; font label 18;select atomno=7;color black;label %A C-F \u03c3* orbital;');\" alt=\"\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/fluoroethane2.jpg\" width=\"200\" height=\"245\" \/><p id=\"caption-attachment-1892\" class=\"wp-caption-text\">Empty C-F antibonding NBO orbital. Click for 3D<\/p><\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>A filled C-H orbital is shown above on the left, accompanied by an empty C-F \u03c3* orbital on the right which is anti-periplanar to the first. This alignment allows the phases of the two orbitals to overlap maximally (blue-blue on the top, red-red beneath).<\/p>\n<p>The interaction energy between this pair is determined not only by the efficacy of the overlap, but by the energy gap between the two. The smaller the gap, the better the interaction energy (referred to as <strong>E2<\/strong>, in kcal\/mol). For the gauche conformation, the six pairs of orbitals have the following interaction energies; two \u03c3<sub>C-H<\/sub>\/\u03c3*<sub>C-F<\/sub> interactions (illustrated above), 4.9; two \u03c3<sub>C-H<\/sub>\/\u03c3*<sub>C-H <\/sub>2.6 and two \u03c3<sub>C-F<\/sub>\/\u03c3*<sub>C-H<\/sub> 0.8 kcal\/mol. For the anti-periplanar conformation, the terms are four \u03c3<sub>C-H<\/sub>\/\u03c3*<sub>C-H<\/sub> 2.5 and two \u03c3<sub>C-F<\/sub>\/\u03c3*<sub>C-F <\/sub>1.8 kcal\/mol. The two totals (16.6 vs 13.6) indicate that gauche is stabilized more by such interactions.<\/p>\n<p>There is of course a bit more to this story, but I have documented the above here, since I can include an explicit (and rotatable) illustration of the orbitals involved (which \u00a0I have not seen elsewhere). If you want a recipe for generating these orbitals, <a href=\"http:\/\/www.ch.ic.ac.uk\/local\/organic\/conf\/c1_nbo.html\" target=\"_blank\" rel=\"noopener\">go here<\/a>.<\/p>\n<hr \/>\n<h4>Acknowledgments<\/h4>\n<p>This post has been cross-posted in PDF format at <a href=\"https:\/\/doi.org\/10.15200\/winn.143125.51716\" rel=\"noopener\" target=\"_blank\">Authorea<\/a>.<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 1887 -->","protected":false},"excerpt":{"rendered":"<p>Here I offer another spin-off from writing a lecture course on conformational analysis. This is the famous example of why 1,2-difluoroethane adopts a gauche rather than antiperiplanar conformation. One major contribution to the greater stability of the gauche is the stereoelectronic interactions, and this is best probed using the NBO (Natural Bond Orbital) approach of [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[4],"tags":[211,17,212,210,41,2648,213],"ppma_author":[2661],"class_list":["post-1887","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-appropriate-algorithms","tag-conformational-analysis","tag-energy-gap","tag-here-i","tag-interaction-energy","tag-interesting-chemistry","tag-spin-off"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>The conformation of 1,2-difluoroethane - Henry Rzepa&#039;s Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The conformation of 1,2-difluoroethane - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"Here I offer another spin-off from writing a lecture course on conformational analysis. This is the famous example of why 1,2-difluoroethane adopts a gauche rather than antiperiplanar conformation. One major contribution to the greater stability of the gauche is the stereoelectronic interactions, and this is best probed using the NBO (Natural Bond Orbital) approach of [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2010-04-06T11:36:51+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2023-09-16T18:41:48+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The conformation of 1,2-difluoroethane - Henry Rzepa&#039;s Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","og_locale":"en_GB","og_type":"article","og_title":"The conformation of 1,2-difluoroethane - Henry Rzepa&#039;s Blog","og_description":"Here I offer another spin-off from writing a lecture course on conformational analysis. This is the famous example of why 1,2-difluoroethane adopts a gauche rather than antiperiplanar conformation. One major contribution to the greater stability of the gauche is the stereoelectronic interactions, and this is best probed using the NBO (Natural Bond Orbital) approach of [&hellip;]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","og_site_name":"Henry Rzepa&#039;s Blog","article_published_time":"2010-04-06T11:36:51+00:00","article_modified_time":"2023-09-16T18:41:48+00:00","og_image":[{"url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"The conformation of 1,2-difluoroethane","datePublished":"2010-04-06T11:36:51+00:00","dateModified":"2023-09-16T18:41:48+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887"},"wordCount":409,"commentCount":14,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg","keywords":["appropriate algorithms","conformational analysis","energy gap","Here I","interaction energy","Interesting chemistry","spin-off"],"articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","name":"The conformation of 1,2-difluoroethane - Henry Rzepa&#039;s Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg","datePublished":"2010-04-06T11:36:51+00:00","dateModified":"2023-09-16T18:41:48+00:00","author":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"breadcrumb":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#primaryimage","url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg","contentUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"The conformation of 1,2-difluoroethane"}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa&#039;s Blog","description":"Chemistry with a twist","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Person","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281","name":"Henry Rzepa","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g370be3a7397865e4fd161aefeb0a5a85","url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","caption":"Henry Rzepa"},"description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.","sameAs":["https:\/\/orcid.org\/0000-0002-8635-8390"],"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?author=1"}]}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pDef7-ur","jetpack-related-posts":[],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1887","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1887"}],"version-history":[{"count":9,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1887\/revisions"}],"predecessor-version":[{"id":26476,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1887\/revisions\/26476"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1887"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1887"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1887"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=1887"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}