{"id":16557,"date":"2016-06-18T09:43:30","date_gmt":"2016-06-18T08:43:30","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=16557"},"modified":"2016-06-18T09:43:30","modified_gmt":"2016-06-18T08:43:30","slug":"why-is-the-carbonyl-ir-stretch-in-an-ester-higher-than-in-a-ketone-crystal-structure-data-mining","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=16557","title":{"rendered":"Why is the carbonyl IR stretch in an ester higher than in a ketone: crystal structure data mining."},"content":{"rendered":"
\n

In this post<\/a>, I pondered upon the C=O infra-red spectroscopic\u00a0properties of esters, and showed three possible electronic influences:<\/p>\n

\"s-cis-ester1\"<\/p>\n

The red (and blue) arrows imply the C-O bond might shorten and the C=O bond would lengthen; the green the reverse. So time for a search of the crystal structure database as a reality check. The query is as follows:<\/p>\n

\"s-cis-ester1\"<\/p>\n

The response shows the bimodal distribution with as expected the s-cis<\/em> conformation dominating. There is indeed a hint that for the s-cis<\/em>, the C-O distance is rather shorter than for the s-trans<\/em> conformation.<\/p>\n

\"s-cis-ester1\"<\/p>\n

Repeating the search, but specifying that the temperature of data acquisition is < 90K, one gets a much clearer indication of the difference in bond lengths.<\/p>\n

\"s-cis-ester1\"<\/p>\n

This alternative representation shows the C-O and the C=O distances, with red indicating s-trans<\/em> and blue indicating s-cis<\/em> conformations (T < 140K). The red dots occupy a bottom right cluster for which the C-O distance is longer and the C=O shorter than the corresponding blue cluster.<\/p>\n

\"s-cis-ester1\"<\/p>\n

Again reducing the temperature of data collection to < 90K shows a rather weak inverse correlation between the two distances for eg the blue dots.<\/p>\n

\"s-cis-ester1\"<\/p>\n

A shame however that this database does not hold IR values for the carbonyl stretches. I am sure correlations must exist, but how to get at them (other than manual collection of data).<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

In this post, I pondered upon the C=O infra-red spectroscopic\u00a0properties of esters, and showed three possible electronic influences: The red (and blue) arrows imply the C-O bond might shorten and the C=O bond would lengthen; the green the reverse. So time for a search of the crystal structure database as a reality check. The query […]<\/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":[1788,1453,1800],"class_list":["post-16557","post","type-post","status-publish","format-standard","hentry","category-chemical-it","category-crystal_structure_mining","tag-ester","tag-functional-groups","tag-infra-red"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-4j3","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/16557","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=16557"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/16557\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=16557"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=16557"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=16557"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}