{"id":21798,"date":"2019-12-28T20:07:44","date_gmt":"2019-12-28T20:07:44","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=21798"},"modified":"2019-12-29T08:04:40","modified_gmt":"2019-12-29T08:04:40","slug":"can-a-carbon-radical-act-as-a-hydrogen-bond-acceptor","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21798","title":{"rendered":"Can a carbon radical act as a hydrogen bond acceptor?"},"content":{"rendered":"
\n

Having shown that carbon as a carbene centre, C:<\/span><\/strong><\/span>\u00a0can act as a hydrogen bond acceptor, as seen from a search of crystal structures, I began to wonder if there is any chance that carbon as a radical centre, C\u2022<\/span><\/span> could do so as well.\u00a0Definitely a subversive thought, since radical centres are supposed to abstract hydrogens rather than to hydrogen bond to them.<\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a>One molecule that emerges from such a search (Query: 10.14469\/hpc\/6572<\/a>) was reported recently as a resonance stabilized radical,[1]<\/a><\/span> with the\u00a0intermolecular hydrogen bond that emerges being from an aryl C-H directed at the carbon radical centre. The length\u00a0(after correction\u00a0by -0.1\u00c5) is typical (this interaction is not noted in the article itself). Most\u00a0of the 31 hits are in fact intra-molecular.<\/p>\n

\"\"<\/a><\/p>\n

\"\"

Click image to view 3D model<\/p><\/div>\n

The spin density arising from the unpaired electron of the radical is indeed delocalised, although the largest part is in a p\u03c0<\/sub> orbital on the carbon radical centre.<\/p>\n

\"\"<\/a><\/p>\n

The molecular electrostatic potential\u00a0(MEP) shows a negative π-potential (attractive to a proton) covering the radical carbon, but also the adjacent boron.<\/p>\n

\"\"<\/a><\/p>\n

These types of hydrogen bond to a carbon radical acceptor are clearly weak (if indeed they are real), but perhaps a balance has to be achieved between two effects: less delocalised carbon radicals might form stronger hydrogen bonds but they will also abstract hydrogen atoms from potential hydrogen bond donors. More highly delocalised radicals are less likely to abstract, but probably also less likely to form strong hydrogen bond acceptors. Nonetheless, one can ask whether a stronger carbon radical hydrogen bond acceptor might be found that exists in that region where abstraction does not occur. As I noted at the start, I am trying to be provocative!<\/p>\n

References<\/h2>\n
  1. T. Kushida, S. Shirai, N. Ando, T. Okamoto, H. Ishii, H. Matsui, M. Yamagishi, T. Uemura, J. Tsurumi, S. Watanabe, J. Takeya, and S. Yamaguchi, \"Boron-Stabilized Planar Neutral \u03c0-Radicals with Well-Balanced Ambipolar Charge-Transport Properties\", Journal of the American Chemical Society<\/i>, vol. 139, pp. 14336-14339, 2017. https:\/\/doi.org\/10.1021\/jacs.7b05471<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    Having shown that carbon as a carbene centre, C:\u00a0can act as a hydrogen bond acceptor, as seen from a search of crystal structures, I began to wonder if there is any chance that carbon as a radical centre, C\u2022 could do so as well.\u00a0Definitely a subversive thought, since radical centres are supposed to abstract hydrogens […]<\/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":[1745,4],"tags":[],"ppma_author":[2661],"class_list":["post-21798","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","category-interesting-chemistry"],"yoast_head":"\nCan a carbon radical act as a hydrogen bond acceptor? - 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=21798\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Can a carbon radical act as a hydrogen bond acceptor? - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Having shown that carbon as a carbene centre, C:\u00a0can act as a hydrogen bond acceptor, as seen from a search of crystal structures, I began to wonder if there is any chance that carbon as a radical centre, C\u2022 could do so as well.\u00a0Definitely a subversive thought, since radical centres are supposed to abstract hydrogens […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21798\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2019-12-28T20:07:44+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2019-12-29T08:04:40+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/query-1.jpg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Can a carbon radical act as a hydrogen bond acceptor? 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Wikipedia asserts that carbon can act as a donor, as we saw in\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/query-1024x598.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":6921,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=6921","url_meta":{"origin":21798,"position":2},"title":"Transition state models for Baldwin dig(onal) ring closures.","author":"Henry Rzepa","date":"June 10, 2012","format":false,"excerpt":"This is a continuation of the previous post exploring the transition state geometries of various types of ring closure as predicted by \u00a0Baldwin's rules. I had dealt with bond formation to a trigonal (sp2) carbon; now I add a digonal (sp) example (see an interesting literature variation).\u00a0 As before, I\u2026","rel":"","context":"In \"Baldwins rules\"","block_context":{"text":"Baldwins rules","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=baldwins-rules"},"img":{"alt_text":"","src":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/06\/baldwin-dig.svg","width":350,"height":200},"classes":[]},{"id":9459,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9459","url_meta":{"origin":21798,"position":3},"title":"The conformational preference of s-cis amides.","author":"Henry Rzepa","date":"February 10, 2013","format":false,"excerpt":"Amides with an H-N group are a component of the peptide linkage\u00a0(O=C-NH). Here I ask what the conformation (it could also be called a configuration) about the C-N bond is. 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Could it be that again, the diol is somehow preferentially stabilised compared to the carbonyl precursor\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/03\/formaldehyde-diol.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":18822,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=18822","url_meta":{"origin":21798,"position":5},"title":"Hydrogen capture by boron: a crazy reaction path!","author":"Henry Rzepa","date":"September 21, 2017","format":false,"excerpt":"A recent article reports, amongst other topics, a computationally modelled reaction involving the capture of molecular hydrogen using a substituted borane (X=N, Y=C). 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