{"id":14543,"date":"2015-09-05T11:17:55","date_gmt":"2015-09-05T10:17:55","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=14543"},"modified":"2015-09-05T11:17:55","modified_gmt":"2015-09-05T10:17:55","slug":"%cf%80-resonance-in-thioamides-a-crystallographic-diff-with-amides","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=14543","title":{"rendered":"\u03c0-Resonance in thioamides: a crystallographic &#8220;diff&#8221; with amides."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"14543\">\n<p>The\u00a0previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides.<\/p>\n<p><img data-recalc-dims=\"1\" decoding=\"async\" src=\"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/09\/SAmide-def.jpg?w=400\" alt=\"Scheme\"  \/><\/p>\n<p>Here is the torsional analysis around the C-N bond. The &#8220;diff&#8221; (difference) is that almost all the hits are concentrated into angles of 0\u00b0 or 180\u00b0; the twist about the C-N bond\u00a0from co-planarity is much less if S is present. This is normally explained in terms of Sp<sub>\u03c0<\/sub>-Cp<sub>\u03c0<\/sub> overlaps being less favourable than Op<sub>\u03c0<\/sub>-Cp<sub>\u03c0<\/sub> ones owing to the mismatch in the size of the atomic orbital for S and C. Hence the resonance which reduces the C=S double bond character in favour of greater C=N character is enhanced\u00a0compared to O.<\/p>\n<p><img data-recalc-dims=\"1\" decoding=\"async\" src=\"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/09\/SAmide-torsions1.jpg?w=440\" alt=\"Scheme\"  \/><\/p>\n<p>A consequence is that the nitrogen atom is less easily deformed from planarity in a thioamide. Notice also that at the hotspot, the C=N distance is ~1.32\u00c5 compared to 1.34\u00c5 for a regular amide.<\/p>\n<p><img data-recalc-dims=\"1\" decoding=\"async\" src=\"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/09\/SAmide-torsions2.jpg?w=440\" alt=\"Scheme\"  \/><\/p>\n<p>This emerges from the plot below as well; the range of values for the C-N bond is reduced compared to amides, but the diagonal trend that as the C=N bond gets longer so the C-S gets shorter is still seen.<\/p>\n<p><img data-recalc-dims=\"1\" decoding=\"async\" src=\"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/09\/SAmide-torsions3.jpg?w=440\" alt=\"Scheme\"  \/><\/p>\n<p>All these trends are described qualitatively in most text books of organic chemistry, but one never sees statistical evidence for them. And it truly only takes 5-10 minutes to produce.<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 14543 -->","protected":false},"excerpt":{"rendered":"<p>The\u00a0previous post explored the structural features of amides. Here I compare the analysis with that for the closely related thioamides. Here is the torsional analysis around the C-N bond. The &#8220;diff&#8221; (difference) is that almost all the hits are concentrated into angles of 0\u00b0 or 180\u00b0; the twist about the C-N bond\u00a0from co-planarity is much [&hellip;]<\/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":[3,1754],"tags":[1557,1453,1614],"class_list":["post-14543","post","type-post","status-publish","format-standard","hentry","category-chemical-it","category-crystal_structure_mining","tag-amide","tag-functional-groups","tag-thioamide"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-3Mz","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/14543","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=14543"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/14543\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=14543"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14543"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14543"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}