{"id":6279,"date":"2012-02-20T06:45:59","date_gmt":"2012-02-20T06:45:59","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=6279"},"modified":"2012-02-20T09:44:13","modified_gmt":"2012-02-20T09:44:13","slug":"e2-elimination-vs-ring-contraction-anti-periplanarity-in-action","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279","title":{"rendered":"E2 elimination vs ring contraction: anti-periplanarity in action."},"content":{"rendered":"
\n

The anti-periplanar principle permeates organic reactivity. Here I pick up on an example of the antiperiplanar E2 elimination (below, blue) by comparing it to a competing reaction involving a [1,2] antiperiplanar migration (red).<\/p>\n

\"\"<\/a><\/p>\n

The relative rates of these two processes will depend on several factors such as the ability of Cl to donate electrons (red) vs the basicity of the chloride anion (blue) and of course solvent polarity. It is the balance between these two mechanisms that caught Barton’s eye and helped him formulate his ideas about conformational analysis. Calculations (\u03c9B97XD\/6-311G(d,p)\/SCRF=water) help reveal the basic features of the competition; details can be found for the ring contraction<\/a> and E2 elimination<\/a>.<\/p>\n\n\n\n\n
Ring contraction<\/th>\nE2 Elimination<\/th>\n<\/tr>\n
\"\"

Ring contraction. Click for 3D.<\/p><\/div><\/td>\n

\"\"

E2 elimination. Click for 3D.<\/p><\/div><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

If you focus on the dashed bonds<\/em><\/strong>, you can easily identify the anti-periplanar<\/em><\/strong> components for each reaction. In this specific example, the E2 reaction wins out over the ring contraction\/migration by \u0394\u0394G298<\/sub> = 17.6 kcal\/mol. (One of) the orbital interactions responsible for the antiperiplanar migration is shown below.<\/p>\n

\"\"

The orbital overlap in the app migration. Click for 3D<\/p><\/div>The Intrinsic reaction coordinates for the E2 elimination and migration are shown below, oriented to demonstrate their app nature.<\/p>\n\n\n\n
\"\"<\/a><\/td>\n\"\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

You might notice that via<\/em> these posts, I am gradually building up a library of transition states for taught reactions. Still a few to go however!<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

The anti-periplanar principle permeates organic reactivity. Here I pick up on an example of the antiperiplanar E2 elimination (below, blue) by comparing it to a competing reaction involving a [1,2] antiperiplanar migration (red). The relative rates of these two processes will depend on several factors such as the ability of Cl to donate electrons (red) […]<\/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":[],"tags":[17,373],"ppma_author":[2661],"class_list":["post-6279","post","type-post","status-publish","format-standard","hentry","tag-conformational-analysis","tag-tutorial-material"],"yoast_head":"\nE2 elimination vs ring contraction: anti-periplanarity in action. - Henry Rzepa'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=6279\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"E2 elimination vs ring contraction: anti-periplanarity in action. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"The anti-periplanar principle permeates organic reactivity. Here I pick up on an example of the antiperiplanar E2 elimination (below, blue) by comparing it to a competing reaction involving a [1,2] antiperiplanar migration (red). The relative rates of these two processes will depend on several factors such as the ability of Cl to donate electrons (red) […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2012-02-20T06:45:59+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2012-02-20T09:44:13+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg\" \/>\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=\"1 minute\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"E2 elimination vs ring contraction: anti-periplanarity in action. - Henry Rzepa'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=6279","og_locale":"en_GB","og_type":"article","og_title":"E2 elimination vs ring contraction: anti-periplanarity in action. - Henry Rzepa's Blog","og_description":"The anti-periplanar principle permeates organic reactivity. Here I pick up on an example of the antiperiplanar E2 elimination (below, blue) by comparing it to a competing reaction involving a [1,2] antiperiplanar migration (red). The relative rates of these two processes will depend on several factors such as the ability of Cl to donate electrons (red) […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279","og_site_name":"Henry Rzepa's Blog","article_published_time":"2012-02-20T06:45:59+00:00","article_modified_time":"2012-02-20T09:44:13+00:00","og_image":[{"url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"1 minute"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"E2 elimination vs ring contraction: anti-periplanarity in action.","datePublished":"2012-02-20T06:45:59+00:00","dateModified":"2012-02-20T09:44:13+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279"},"wordCount":266,"commentCount":1,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg","keywords":["conformational analysis","Tutorial material"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279","name":"E2 elimination vs ring contraction: anti-periplanarity in action. - Henry Rzepa's Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg","datePublished":"2012-02-20T06:45:59+00:00","dateModified":"2012-02-20T09:44:13+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=6279#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#primaryimage","url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg","contentUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6279#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"E2 elimination vs ring contraction: anti-periplanarity in action."}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa'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\/pDef7-1Dh","jetpack-related-posts":[{"id":6205,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6205","url_meta":{"origin":6279,"position":0},"title":"An orbital analysis of the stereochemistry of the E2 elimination reaction","author":"Henry Rzepa","date":"February 4, 2012","format":false,"excerpt":"The so-called E2 elimination mechanism is another one of those mainstays of organic chemistry. It is important because it introduces the principle that anti-periplanarity of the reacting atoms is favoured over other orientations such as the syn-periplanar form; Barton used this principle to great effect in developing the theory of\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/E2.svg","width":350,"height":200},"classes":[]},{"id":6262,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6262","url_meta":{"origin":6279,"position":1},"title":"An exothermic E2 elimination: an unusual intrinsic reaction coordinate.","author":"Henry Rzepa","date":"February 6, 2012","format":false,"excerpt":"The previous post explored why E2 elimination reactions occur with an antiperiplanar geometry for the transition state. Here I have tweaked the initial reactant to make the overall reaction exothermic rather than endothermic as it was before. The change is startling. The exothermicity is of course due to the aromatisation\u2026","rel":"","context":"In \"conformational analysis\"","block_context":{"text":"conformational analysis","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=conformational-analysis"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/E2-benzo.svg","width":350,"height":200},"classes":[]},{"id":1887,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=1887","url_meta":{"origin":6279,"position":2},"title":"The conformation of 1,2-difluoroethane","author":"Henry Rzepa","date":"April 6, 2010","format":false,"excerpt":"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\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/04\/difluoroethane.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":9459,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9459","url_meta":{"origin":6279,"position":3},"title":"The conformational preference of s-cis amides.","author":"Henry Rzepa","date":"February 10, 2013","format":false,"excerpt":"Amides with an H-N group are a component of the peptide linkage\u00a0(O=C-NH). Here I ask what the conformation (it could also be called a configuration) about the C-N bond is. A search of the following type can be defined: The dihedral shown is for H-N-C=O (but this is equivalent to\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"cis-amide","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/02\/cis-amide.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":9572,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9572","url_meta":{"origin":6279,"position":4},"title":"A to-and-fro of electrons operating in s-cis esters.","author":"Henry Rzepa","date":"February 21, 2013","format":false,"excerpt":"I conclude my exploration of conformational preferences by taking a look at esters. As before, I start with a search definition, the ester being restricted to one bearing only sp3 carbon centers. The result of such a search is pretty clear-cut; they all exist in just one conformation, the s-cis,\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"s-cis-ester-torsion-search","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/02\/s-cis-ester-torsion-search.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":4038,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4038","url_meta":{"origin":6279,"position":5},"title":"Updating a worked problem in conformational analysis. Part 2: an answer.","author":"Henry Rzepa","date":"May 17, 2011","format":false,"excerpt":"The previous post set out a problem in conformational analysis. Here is my take, which includes an NCI (non-covalent interaction) display as discussed in another post. The lowest energies of the four diastereomers A-D, each in two conformations (1\/2) were calculated at the \u03c9B97D\/6-311G(d,p)\/SCRF=ethanol level, and are shown here relative\u2026","rel":"","context":"In \"conformational analysis\"","block_context":{"text":"conformational analysis","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=conformational-analysis"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/05\/problem_sheet_answer42.jpg?resize=350%2C200","width":350,"height":200},"classes":[]}],"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\/6279","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=6279"}],"version-history":[{"count":25,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6279\/revisions"}],"predecessor-version":[{"id":6311,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6279\/revisions\/6311"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6279"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6279"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6279"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=6279"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}