{"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":"2012-02-20T06:45:59","modified_gmt":"2012-02-20T06:45:59","slug":"e2-elimination-vs-ring-contraction-anti-periplanarity-in-action","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2012\/02\/20\/e2-elimination-vs-ring-contraction-anti-periplanarity-in-action\/","title":{"rendered":"E2 elimination vs ring contraction: anti-periplanarity in action."},"content":{"rendered":"<p>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<p style=\"text-align: center;\"><a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-6280\" title=\"Ring\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.svg\" alt=\"\" width=\"373\" height=\"295\" \/><\/a><\/p>\n<p>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&#8217;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 <a href=\"http:\/\/hdl.handle.net\/10042\/to-12723\" target=\"_blank\">ring contraction<\/a> and <a href=\"http:\/\/hdl.handle.net\/10042\/to-12724\" target=\"_blank\">E2 elimination<\/a>.<\/p>\n<table style=\"margin-left: auto; margin-right: auto;\" border=\"1\">\n<tbody>\n<tr>\n<th>Ring contraction<\/th>\n<th>E2 Elimination<\/th>\n<\/tr>\n<tr>\n<td><figure id=\"attachment_6284\" aria-describedby=\"caption-attachment-6284\" style=\"width: 200px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" class=\" wp-image-6284 \" title=\"ring\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('yellow');jmolApplet([450,450],'load wp-content\/uploads\/2012\/02\/Ring.log;frame 9; zoom 100;connect (atomno=3) (atomno=5) partial;connect (atomno=4) (atomno=5) partial;connect (atomno=3) (atomno=17) partial;vectors on;vectors 4;vectors scale 5.0; color vectors red; vibration 20;animation mode loop;measure 5 4 3 17;');\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/ring.jpg\" alt=\"\" width=\"200\" \/><figcaption id=\"caption-attachment-6284\" class=\"wp-caption-text\">Ring contraction. Click for 3D.<\/figcaption><\/figure><\/td>\n<td><figure id=\"attachment_6285\" aria-describedby=\"caption-attachment-6285\" style=\"width: 200px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" class=\"size-full wp-image-6285\" title=\"E2\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('yellow');jmolApplet([450,450],'load wp-content\/uploads\/2012\/02\/E2.log;frame 3; zoom 100;connect (atomno=4) (atomno=18) partial;connect (atomno=3) (atomno=16) partial;connect (atomno=16) (atomno=19) partial;vectors on;vectors 4;vectors scale 5.0; color vectors blue; vibration 20;animation mode loop;measure 18 4 3 16;');\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/E2.jpg\" alt=\"\" width=\"200\" \/><figcaption id=\"caption-attachment-6285\" class=\"wp-caption-text\">E2 elimination. Click for 3D.<\/figcaption><\/figure><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>If you focus on the <strong><em>dashed bonds<\/em><\/strong>, you can easily identify the <strong><em>anti-periplanar<\/em><\/strong> components for each reaction. In this specific example, the E2 reaction wins out over the ring contraction\/migration by \u0394\u0394G<sub>298<\/sub> = 17.6 kcal\/mol. (One of) the orbital interactions responsible for the antiperiplanar migration is shown below.<\/p>\n<p><figure id=\"attachment_6296\" aria-describedby=\"caption-attachment-6296\" style=\"width: 193px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\" wp-image-6296 \" title=\"Ring-NBO\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2012\/02\/Ring_mo50.xyz;connect (atomno=3) (atomno=5) partial;connect (atomno=4) (atomno=5) partial;connect (atomno=3) (atomno=17) partial;isosurface color purple orange wp-content\/uploads\/2012\/02\/Ring_mo50.jvxl translucent;isosurface append wp-content\/uploads\/2012\/02\/Ring_mo43.jvxl translucent;zoom 120;');\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring-NBO.jpg\" alt=\"\" width=\"193\" height=\"173\" \/><figcaption id=\"caption-attachment-6296\" class=\"wp-caption-text\">The orbital overlap in the app migration. Click for 3D<\/figcaption><\/figure>The Intrinsic reaction coordinates for the E2 elimination and migration are shown below, oriented to demonstrate their app nature.<\/p>\n<table style=\"margin-left: auto; margin-right: auto;\" border=\"1\">\n<tbody>\n<tr>\n<td><a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/E2-ring.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter  wp-image-6303\" title=\"E2-ring\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/E2-ring.gif\" alt=\"\" width=\"212\" height=\"203\" \/><\/a><\/td>\n<td><a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter  wp-image-6305\" title=\"Ring\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/02\/Ring.gif\" alt=\"\" width=\"178\" height=\"139\" \/><\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>You might notice that <em>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","protected":false},"excerpt":{"rendered":"<p>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) [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[647,2489],"class_list":["post-6279","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-conformational-analysis","tag-tutorial-material"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/6279","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=6279"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/6279\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=6279"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=6279"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=6279"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}