{"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:\/\/www.rzepa.net\/blog\/?p=11110","title":{"rendered":"Coarctate reactions as a third fundamental organic-mechanistic type."},"content":{"rendered":"
\n

According to Herges[1]<\/a><\/span>,[2]<\/a><\/span> 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[3]<\/a><\/span> 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.[4]<\/a><\/span><\/p>\n

\"Click

Click for 3D<\/p><\/div>\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

    References<\/h2>\n
    1. R. Herges, \"Coarctate transition states: the discovery of a reaction principle\", Journal of Chemical Information and Computer Sciences<\/i>, vol. 34, pp. 91-102, 1994. https:\/\/doi.org\/10.1021\/ci00017a011<\/a>\n\n<\/li>\n
    2. B.S. Young, R. Herges, and M.M. Haley, \"Coarctate cyclization reactions: a primer\", Chemical Communications<\/i>, vol. 48, pp. 9441, 2012. https:\/\/doi.org\/10.1039\/c2cc34026g<\/a>\n\n<\/li>\n
    3. C. Berger, C. Bresler, U. Dilger, D. Geuenich, R. Herges, H. R\u00f6ttele, and G. Schr\u00f6der, \"A Spontaneous Fragmentation: From the Criegee Zwitterion to Coarctate M\u00f6bius Aromaticity\", Angewandte Chemie International Edition<\/i>, vol. 37, pp. 1850-1853, 1998. https:\/\/doi.org\/10.1002\/(sici)1521-3773(19980803)37:13\/14<1850::aid-anie1850>3.0.co;2-b<\/a>\n\n<\/li>\n
    4. H.S. Rzepa, \"Gaussian Job Archive for C4H6O3\", 2013. https:\/\/doi.org\/10.6084\/m9.figshare.787693<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      According to Herges, 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 illustrating: It […]<\/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,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1085],"tags":[1125],"class_list":["post-11110","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2","tag-ozonolysis"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-2Tc","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11110","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=11110"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11110\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11110"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11110"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11110"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}