{"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":"2017-11-21T13:01:11","modified_gmt":"2017-11-21T13:01:11","slug":"elongating-a-n-b-single-bond-is-much-easier-than-stretching-a-c-c-single-bond","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/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\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,"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":[1745],"tags":[194,2301,1402,557,1395,1519,295,1871,1512,734],"ppma_author":[2661],"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"],"yoast_head":"\nElongating an N-B single bond is much easier than stretching a C-C single bond. - 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=18950\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Elongating an N-B single bond is much easier than stretching a C-C single bond. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"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). 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But this arose from highly unusual bonding giving rise not to a single bond order but one closer to one half! How long can a\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"long-cc","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2016\/11\/long-cc-1024x757.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":17122,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17122","url_meta":{"origin":18950,"position":1},"title":"Long C=C bonds.","author":"Henry Rzepa","date":"December 1, 2016","format":false,"excerpt":"Following on from a search for long C-C bonds, here is the same repeated for C=C double bonds. The query restricts the search to each carbon having just two non-metallic substituents. To avoid conjugation with these, they each are 4-coordinated; the carbons themselves are three-coordinated. Further constraints are the usual\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"sq","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2016\/12\/sq-1024x415.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":16518,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16518","url_meta":{"origin":18950,"position":2},"title":"A wider look at \u03c0-complex metal-alkene (and alkyne) compounds.","author":"Henry Rzepa","date":"June 13, 2016","format":false,"excerpt":"Previously, I looked at the historic origins of the so-called \u03c0-complex theory of metal-alkene complexes. Here I follow this up with some data mining of the crystal structure database for such structures. Alkene-metal \"\u03c0-complexes\" have what might be called a representational problem; they do not happily fit into the standard\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":17992,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17992","url_meta":{"origin":18950,"position":3},"title":"The conformation of enols: revealed and explained.","author":"Henry Rzepa","date":"April 6, 2017","format":false,"excerpt":"Enols are simple compounds with an OH group as a substituent on a C=C double bond and with a very distinct conformational preference for the OH group. Here I take a look at this preference as revealed by crystal structures, with the theoretical explanation. First, a search of the Cambridge\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2017\/04\/All-1024x948.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":14485,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14485","url_meta":{"origin":18950,"position":4},"title":"A visualisation of the effects of conjugation; dienes and biaryls.","author":"Henry Rzepa","date":"August 25, 2015","format":false,"excerpt":"Here is another exploration of simple chemical concepts using crystal structures. Consider a simple diene: how does the central C-C bond length respond to the torsion angle between the two C=C bonds? The search of the CSD (Cambridge structure database) is constrained to R < 5%, no errors and no\u2026","rel":"","context":"In "Chemical IT"","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":17168,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17168","url_meta":{"origin":18950,"position":5},"title":"Molecule of the year? “CrN123”, a molecule with three different types of Cr-N bond.","author":"Henry Rzepa","date":"December 16, 2016","format":false,"excerpt":"Here is a third candidate for the C&EN \"molecule of the year\" vote. This one was shortlisted because it is the first example of a metal-nitrogen complex exhibiting single, double and triple bonds from different nitrogens to the same metal (XUZLUB has a 3D display available at DOI: 10.5517\/CC1JYY6M). Since\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"","width":0,"height":0},"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\/18950","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=18950"}],"version-history":[{"count":18,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18950\/revisions"}],"predecessor-version":[{"id":19093,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18950\/revisions\/19093"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18950"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18950"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18950"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=18950"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}