{"id":11110,"date":"2013-09-04T14:52:03","date_gmt":"2013-09-04T13:52:03","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=11110"},"modified":"2013-09-04T14:52:03","modified_gmt":"2013-09-04T13:52:03","slug":"coarctate-reactions-as-a-third-fundamental-organic-mechanistic-type","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2013\/09\/04\/coarctate-reactions-as-a-third-fundamental-organic-mechanistic-type\/","title":{"rendered":"Coarctate reactions as a third fundamental organic-mechanistic type."},"content":{"rendered":"

According to Herges[cite]10.1021\/ci00017a011[\/cite],[cite]10.1039\/c2cc34026g[\/cite] the mechanism of single-step (concerted) reactions can be divided into three basic types; linear<\/strong> (e.g.<\/em> substitution, elimination etc), pericyclic<\/strong> (e.g.<\/em> Diels Alder) and a third much rarer, and hence very often overlooked type that was named coarctate<\/strong>. This is based on the topology of\u00a0bond redistribution patterns, an explicit real example[cite]bhsn4t[\/cite] illustrating:<\/p>\n

\"coarctate\"<\/p>\n

It happens that this reaction bears a close similarity to epoxidation using peracid<\/a>, the characteristic feature being that the central (spiro) atom has two bonds forming to it and two bonds breaking from it in both reactions.\u2020,\u2021<\/sup> I had noted for the latter reaction that in fact the bond redistribution, although concerted, was asynchronous. This asynchrony was represented by the green arrows preceding the blue ones (or vice-versa<\/em> for the reverse reaction).<\/p>\n

\"peracid1\"<\/a><\/p>\n

So here I decided to investigate if the same might be true of the coarctate reaction shown above (\u03c9B97XD\/6-311G(d,p)\/SCRF=water.[cite]10.6084\/m9.figshare.787693[\/cite]<\/p>\n

\"Click
Click for 3D<\/figcaption><\/figure>\n

The transition state is indeed interestingly asynchronous. The O-O bond (shown green above) is clearly the first to break; neither of the C-C bonds has really started to do so at the transition state. But the process remains resolutely concerted.<\/p>\n

\"coarctate\"<\/p>\n

\"coarc-IRC\"<\/p>\n

\"coarc-IRCG\"\u00a0<\/p>\n

The IRC above shows clearly that the reaction has a room-temperature barrier (i.e.<\/em> it is a very facile process). But missing really from this process is any hidden intermediate either (there is the merest hint at IRC = -2). So this reaction is interesting for<\/p>\n

    \n
  1. its classification apart from the normal two types of organic mechanism, as a coarctate type<\/li>\n
  2. Its asynchrony in the bond redistributions<\/li>\n
  3. but this asynchrony not resulting in any hidden intermediates.<\/li>\n<\/ol>\n
    \n

    \u2020<\/sup> Another example was the topic of this post<\/a>.<\/p>\n

    \u2021<\/sup> One can contrive an even higher-order reaction<\/a> (thus far un-named) in which (formally) three bonds break and three bonds form at a single atom.<\/p>\n","protected":false},"excerpt":{"rendered":"

    According to Herges[cite]10.1021\/ci00017a011[\/cite],[cite]10.1039\/c2cc34026g[\/cite] the mechanism of single-step (concerted) reactions can be divided into three basic types; linear (e.g. substitution, elimination etc), pericyclic (e.g. Diels Alder) and a third much rarer, and hence very often overlooked type that was named coarctate. This is based on the topology of\u00a0bond redistribution patterns, an explicit real example[cite]bhsn4t[\/cite] illustrating: It […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13],"tags":[1858],"class_list":["post-11110","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2","tag-ozonolysis"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/11110","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=11110"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/11110\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=11110"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=11110"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=11110"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}