{"id":4254,"date":"2011-05-31T13:05:16","date_gmt":"2011-05-31T13:05:16","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=4254"},"modified":"2011-05-31T13:05:16","modified_gmt":"2011-05-31T13:05:16","slug":"conformational-restriction-involving-formyl-ch-f-hydrogen-bonds","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=4254","title":{"rendered":"Conformational restriction involving formyl CH…F hydrogen bonds."},"content":{"rendered":"
\n

The title of this post paraphrases E. J. Corey’s article in 1997 (DOI:\u00a010.1016\/S0040-4039(96)02248-4<\/a>) which probed the origins of conformation restriction in aldehydes. The proposal was of (then) unusual hydrogen bonding between the O=C-H…F-B groups. Here I explore whether the NCI (non-covalent-interaction) method can be used to cast light on this famous example of how unusual interactions might mediate selectivity in organic reactions.<\/p>\n

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Crystal structure of RUGYEX. Click for 3D<\/p><\/div>The crystal structure revealed a fixed syn orientation between one B-F bond and the formyl C-H bond, with a distance of ~2.36\u00c5 (using un-normalised C-H lengths), compared with a value of 2.55\u00c5 for the vdW sum. Since hydrogen bonds to fluorine are quite rare, it seems worth applying the NCI method (DOI for calculation<\/a>).<\/p>\n

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NCI surfaces for RUGYEX. click for 3D.<\/p><\/div>The result indeed shows a strongly blue (= attractive) interaction surface for the CH…F region, and only a tiny one for the adjacent \u00a0H…H region. A welcome surprise however is the \u00a0O…O region, which also shows a distinct (strong) attraction. Perhaps this is due to the presence of the electron withdrawing BF3 group on one of the oxygens. This could also be regarded as a through-space anomeric effect, from one oxygen donating into the \u00a0O-B \u03c3* orbital. Such through space<\/em>anomeric effects (they are normally propagated through bonds, as in sugars) are probably more common than we believe.<\/p>\n

This result nicely illustrates the utility of the NCI method; it brings an immediate visual impact, which serves to highlight interactions which otherwise might be ignored.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

The title of this post paraphrases E. J. Corey’s article in 1997 (DOI:\u00a010.1016\/S0040-4039(96)02248-4) which probed the origins of conformation restriction in aldehydes. The proposal was of (then) unusual hydrogen bonding between the O=C-H…F-B groups. Here I explore whether the NCI (non-covalent-interaction) method can be used to cast light on this famous example of how unusual […]<\/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":[6],"tags":[108,515,523,216],"class_list":["post-4254","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-conformational-analysis","tag-corey","tag-formyl-hydrogen","tag-julia-contreras-garcia"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-16C","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4254","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=4254"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/4254\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4254"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4254"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4254"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}