{"id":12810,"date":"2014-08-06T15:03:05","date_gmt":"2014-08-06T14:03:05","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=12810"},"modified":"2014-08-06T15:08:06","modified_gmt":"2014-08-06T14:08:06","slug":"using-a-polar-bond-to-flip-a-follow-up-project","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810","title":{"rendered":"Using a polar bond to flip: a follow up project."},"content":{"rendered":"
\n

In my earlier post<\/a> on the topic, I discussed how inverting the polarity of the C-X bond from X=O to X=Be could flip the stereochemical course of the electrocyclic pericyclic reaction of a divinyl system. An obvious question would be: what happens at the half way stage, ie X=CH2<\/sub>? Well, here is the answer. \"divinylketon\"<\/a> \"CH2\"<\/a> The reaction occurs in two stages (\u03c9B97XD\/6-311G(d,p)\/SCRF=dichloromethane)[1]<\/a><\/span> but overall is a concerted, albeit asynchronous, reaction. The initial stage is a conrotatory ring closure (as observed with X=O but opposite to X=Be), and reaching what we will call a HI<\/strong> (hidden intermediate<\/em>). This HI clearly has zwitterionic character, and manifests its presence most obviously at IRC = -3.5 below. \"CH2\"<\/a>\"CH2G\"<\/a> The polarity of this HI is revealed by the dipole moment (6D) and molecular electrostatic potentials, below. The dipole vector goes from -ve to +ve, and the MEP clearly reveals the polarity below. \"cd7\"<\/a> \"C2-MEP\"<\/a> This ionic HI however is not stable, and in the second stage of the reaction collapses to the neutral bicyclic hydrocarbon shown below. Overall, it amounts to a \u00a02+2 cycloaddition, but with a very unusual pathway in which one C-C bond is very much formed before the other (which is how the reaction escapes the clutches of the Woodward-Hoffmann forbidden-ness). \"cd8\"<\/a> Why is all this worth this follow-up? Well, one can now start to “design” the reaction. All three carbon atoms with formal charges can be stabilised or destabilised with appropriate substituents. It should not be too difficult to stabilise out the HI into just an I(intermediate), or indeed to remove it from the profile. Nice perhaps for a group of students, who can partition up the substituents amongst themselves and discover if they have the desired effect. And would any of this tinkering change the stereochemical outcome?<\/p>\n

References<\/h2>\n
  1. H.S. Rzepa, \"Gaussian Job Archive for C6H8\", 2014. https:\/\/doi.org\/10.6084\/m9.figshare.1128205<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    In my earlier post on the topic, I discussed how inverting the polarity of the C-X bond from X=O to X=Be could flip the stereochemical course of the electrocyclic pericyclic reaction of a divinyl system. An obvious question would be: what happens at the half way stage, ie X=CH2? Well, here is the answer. The […]<\/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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[559],"tags":[1249],"ppma_author":[2661],"class_list":["post-12810","post","type-post","status-publish","format-standard","hentry","category-pericyclic","tag-hawaii"],"yoast_head":"\nUsing a polar bond to flip: a follow up project. - 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=12810\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Using a polar bond to flip: a follow up project. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"In my earlier post on the topic, I discussed how inverting the polarity of the C-X bond from X=O to X=Be could flip the stereochemical course of the electrocyclic pericyclic reaction of a divinyl system. An obvious question would be: what happens at the half way stage, ie X=CH2? Well, here is the answer. The […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2014-08-06T14:03:05+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2014-08-06T14:08:06+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/08\/divinylketon.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=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Using a polar bond to flip: a follow up project. - 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=12810","og_locale":"en_GB","og_type":"article","og_title":"Using a polar bond to flip: a follow up project. - Henry Rzepa's Blog","og_description":"In my earlier post on the topic, I discussed how inverting the polarity of the C-X bond from X=O to X=Be could flip the stereochemical course of the electrocyclic pericyclic reaction of a divinyl system. An obvious question would be: what happens at the half way stage, ie X=CH2? Well, here is the answer. The […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810","og_site_name":"Henry Rzepa's Blog","article_published_time":"2014-08-06T14:03:05+00:00","article_modified_time":"2014-08-06T14:08:06+00:00","og_image":[{"url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/08\/divinylketon.svg","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=12810#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Using a polar bond to flip: a follow up project.","datePublished":"2014-08-06T14:03:05+00:00","dateModified":"2014-08-06T14:08:06+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810"},"wordCount":317,"commentCount":0,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/08\/divinylketon.svg","keywords":["Hawaii"],"articleSection":["pericyclic"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12810","name":"Using a polar bond to flip: a follow up project. - 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This was followed up by exploring what\u00a0happens at the half way stage, i.e. X=CH2,\u2026","rel":"","context":"In "pericyclic"","block_context":{"text":"pericyclic","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=559"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":12782,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12782","url_meta":{"origin":12810,"position":1},"title":"Using a polar bond to flip the (stereochemical) outcome of a pericyclic reaction.","author":"Henry Rzepa","date":"August 4, 2014","format":false,"excerpt":"The outcome of pericyclic reactions con depend most simply on three conditions, any two of which determine the third. Whether the catalyst is \u0394 or h\u03bd (heat or light), the topology determining any stereochemistry and the participating electron count (4n+2\/4n). It is always neat to conjure up a simple switch\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":"","width":0,"height":0},"classes":[]},{"id":11642,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=11642","url_meta":{"origin":12810,"position":2},"title":"Avoided (pericyclic) anti-aromaticity: Reactions of t-butyl-hydroxycarbene.","author":"Henry Rzepa","date":"November 13, 2013","format":false,"excerpt":"Not long ago, I described a cyclic carbene in which elevating the carbene lone pair into a \u03c0-system transformed it from a formally 4n-antiaromatic \u03c0-cycle into a 4n+2 aromatic \u03c0-cycle. From an entirely different area of chemistry, another example of this behaviour emerges; Schreiner's trapping and reactions of t-butyl-hydroxycarbene, as\u2026","rel":"","context":"In "pericyclic"","block_context":{"text":"pericyclic","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=559"},"img":{"alt_text":"H-mig","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/11\/H-mig.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":4592,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4592","url_meta":{"origin":12810,"position":3},"title":"The stereochemistry of [8+2] pericyclic cycloadditions.","author":"Henry Rzepa","date":"July 10, 2011","format":false,"excerpt":"Steve Bachrach has blogged on the reaction shown below. If it were a pericyclic cycloaddition, both new bonds would form simultaneously, as shown with the indicated arrow pushing. Ten electrons would be involved, and in theory, the transition state would have 4n+2 aromaticity. In fact\u00a0Fernandez, Sierra and Torres have reported\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.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/07\/2%2B8.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":6124,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6124","url_meta":{"origin":12810,"position":4},"title":"Secrets of a university tutor: dissection of a reaction mechanism. Part 2, the stereochemistry.","author":"Henry Rzepa","date":"January 30, 2012","format":false,"excerpt":"In the previous post, I went over how a reaction can be stripped down to basic components. That exercise was essentially a flat one in two dimensions, establishing only what connections between atoms are made or broken. Here we look at the three dimensional arrangements. It all boils down to\u2026","rel":"","context":"In \"pericyclic\"","block_context":{"text":"pericyclic","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=pericyclic"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/01\/pericyclic-tutorial_s.svg","width":350,"height":200},"classes":[]},{"id":20354,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20354","url_meta":{"origin":12810,"position":5},"title":"Epoxidation of ethene: a new substituent twist.","author":"Henry Rzepa","date":"December 21, 2018","format":false,"excerpt":"Five years back,\u00a0I speculated about the mechanism of the epoxidation of ethene by a peracid, concluding that kinetic isotope effects provided interesting evidence that this mechanism is highly asynchronous and involves a so-called \"hidden intermediate\". Here I revisit this reaction in which a small change is applied to the atoms\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\/2018\/12\/imine2.gif?resize=350%2C200&ssl=1","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\/12810","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=12810"}],"version-history":[{"count":5,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/12810\/revisions"}],"predecessor-version":[{"id":12821,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/12810\/revisions\/12821"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=12810"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=12810"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=12810"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=12810"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}