{"id":18950,"date":"2017-10-24T17:29:26","date_gmt":"2017-10-24T16:29:26","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=18950"},"modified":"2017-10-24T17:29:26","modified_gmt":"2017-10-24T16:29:26","slug":"elongating-a-n-b-single-bond-is-much-easier-than-stretching-a-c-c-single-bond","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=18950","title":{"rendered":"Elongating an N-B single bond is much easier than stretching a C-C single bond."},"content":{"rendered":"
\n

An N-B single bond is iso-electronic to a C-C single bond, as per below. So here is a simple question: what form does the distribution of the lengths of these two bonds take, as obtained from crystal structures?\u00a0<\/p>\n

\"\" The Conquest search query is very simple (no disorder, no errors).\"\"<\/p>\n

When applied to the Cambridge structure database (CSD) the following two distributions are obtained. That for carbon is pretty symmetric with the peak at ~1.53\u00c5 but with rather faster decay in the region >1.6\u00c5 compared with the region <1.46\u00c5 (the latter may be caused by hyperconjugation shortening the C-C bond).<\/p>\n

\"\"<\/p>\n

In contrast, the iso-electronic N-B distribution is more asymmetric about the peak of 1.56\u00c5, exhibiting a long tail beyond 1.63\u00c5, up to a value of 1.825\u00c5.<\/p>\n

\"\"<\/p>\n

The molecule with that longest N-B bond (1.825\u00c5) is shown below; UWOHUK, Data DOI: 10.5517\/ccwcwlp<\/a>. This by the way is no crystal artefact; a calculation\u00a0(\u03c9B97XD\/6-311G(d,p), Data DOI: 10.14469\/hpc\/3202<\/a>) gives a calculated length of 1.81\u00c5, with a N-B bond order of 0.48.\"\"<\/a><\/p>\n

Stretching a C-C bond heterolytically requires charge separation (a relatively unfavourable process) and likewise homolytic stretching would tend to form a biradical, in effect an excited state and again not favourable. In contrast, elongating the N-B bond reduces (at least formally) any charge separation and allows this heteronuclear pair to sustain (single) bond lengths over the much wider range of ~0.4\u00c5 without requiring biradical formation.<\/p>\n

One might wonder what other single-bonded atoms pairs give such unusually large spans in their bond length distributions.<\/p>\n

\u00a0<\/div>\n
\u00a0<\/div>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

An N-B single bond is iso-electronic to a C-C single bond, as per below. So here is a simple question: what form does the distribution of the lengths of these two bonds take, as obtained from crystal structures?\u00a0 The Conquest search query is very simple (no disorder, no errors). When applied to the Cambridge structure […]<\/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":[1754],"tags":[53,2306,1414,510,1416,1425,111,1881,1500,733],"class_list":["post-18950","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","tag-bond","tag-bond-valence-method","tag-chemical-bond","tag-chemical-bonding","tag-chemistry","tag-covalent-bond","tag-crystal-structure","tag-nature","tag-quantum-chemistry","tag-search-query"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-4VE","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18950","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=18950"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18950\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18950"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18950"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18950"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}