{"id":21772,"date":"2019-12-27T06:57:13","date_gmt":"2019-12-27T06:57:13","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=21772"},"modified":"2019-12-30T11:08:43","modified_gmt":"2019-12-30T11:08:43","slug":"carbon-as-a-hydrogen-bond-acceptor-can-dicarbon-c2-act-in-this-manner","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772","title":{"rendered":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner?"},"content":{"rendered":"
\n

In the previous post<\/a>, I showed that carbon can act as a hydrogen bond acceptor (of a proton) to form strong hydrogen bond complexes. Which brings me to a conceptual connection: can singlet dicarbon form such a hydrogen bond?\u00a0
\n\"\"<\/a><\/p>\n

Dicarbon can be variously represented as above. The first form shows it as a bis-carbene, with an unbonded lone pair of electrons at each end of a carbon double bond. The middle form has emerged in the last ten years or so as a serious alternative to describing the singlet state structure.\u00a0It contains a so-called triple endo<\/em>–<\/strong>bond and one further much weaker exo<\/strong><\/em>-bond (indicated separately by the symbol above the bond), referred to for simplicity as quadruple-bonded dicarbon. The third form would be a triplet biradical with triple bonded carbon. The species is known to be a singlet ground state with a significant excitation energy to the triplet.‡<\/sup> One can then ask the question: would either of these singlet state species be capable of being a hydrogen bond acceptor?<\/p>\n

Time for calculations, at the CCSD(T)\/Def2-TZVPP level using HF as the hydrogen bond donor (to enable advantage to be taken of the axial symmetry), data DOI: 10.14469\/hpc\/6554<\/a>.<\/p>\n

    \n
  1. The singlet quadruple bonded form emerges as 32 kcal\/mol higher in total energy than the singlet dicarbene.<\/li>\n
  2. The quadruple bonded form shows no sign of forming a hydrogen bond. The geometry optimisation curve is shown below followed by the final geometry (\u00c5).\n

    \u00a0\"\"<\/a><\/p>\n

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

  3. The bis-carbene form \u00a0(calculated by a double electron excitation, orbitals 10 to 12 and 11 to 15) DOES form such a complex. The hydrogen bond length (2.04\u00c5) is exactly that found from the crystal structures of the shortest such bonds.\n

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

  4. Two \u00a0of the normal vibrational modes of this species are shown below, being respectively the H…C and C=C stretches (153 and 1394 cm-1<\/sup>). \u00a0\u00a0\"\"<\/a> \"\"<\/a><\/li>\n<\/ol>\n

    So dicarbon CAN form a short hydrogen bond to a donor such as HF, but only in its excited singlet state, which is some 32 kcal\/mol above the quadruple-bonded form. Perhaps because of that fourth bond, the hydrogen bonding ability of this species is entirely inhibited. We have gotten to the point I wanted to reach; an experimental prediction that if singlet dicarbon can ever be trapped in a very inert matrix at very low temperatures in the presence of a hydrogen bond donor, it will not<\/strong> form a hydrogen bond to that donor. That is going to be a difficult experiment, but at least the prediction is out there as a challenge!<\/p>\n

    \n

    ‡<\/sup>At the same level of theory, the triplet 3<\/sup>Σu<\/sub> state is calculated to be 27.0 kcal\/mol higher than the singlet 1<\/sup>Σg<\/sub>.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    In the previous post, I showed that carbon can act as a hydrogen bond acceptor (of a proton) to form strong hydrogen bond complexes. Which brings me to a conceptual connection: can singlet dicarbon form such a hydrogen bond?\u00a0 Dicarbon can be variously represented as above. The first form shows it as a bis-carbene, with […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_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},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[],"ppma_author":[2661],"class_list":["post-21772","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"yoast_head":"\nCarbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner? - 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=21772\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner? - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"In the previous post, I showed that carbon can act as a hydrogen bond acceptor (of a proton) to form strong hydrogen bond complexes. Which brings me to a conceptual connection: can singlet dicarbon form such a hydrogen bond?\u00a0 Dicarbon can be variously represented as above. The first form shows it as a bis-carbene, with […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2019-12-27T06:57:13+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2019-12-30T11:08:43+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg\" \/>\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":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner? - Henry Rzepa's Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772","og_locale":"en_GB","og_type":"article","og_title":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner? - Henry Rzepa's Blog","og_description":"In the previous post, I showed that carbon can act as a hydrogen bond acceptor (of a proton) to form strong hydrogen bond complexes. Which brings me to a conceptual connection: can singlet dicarbon form such a hydrogen bond?\u00a0 Dicarbon can be variously represented as above. The first form shows it as a bis-carbene, with […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772","og_site_name":"Henry Rzepa's Blog","article_published_time":"2019-12-27T06:57:13+00:00","article_modified_time":"2019-12-30T11:08:43+00:00","og_image":[{"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner?","datePublished":"2019-12-27T06:57:13+00:00","dateModified":"2019-12-30T11:08:43+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772"},"wordCount":450,"commentCount":0,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#primaryimage"},"thumbnailUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg","articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772","name":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner? - Henry Rzepa's Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#primaryimage"},"thumbnailUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg","datePublished":"2019-12-27T06:57:13+00:00","dateModified":"2019-12-30T11:08:43+00:00","author":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"breadcrumb":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#primaryimage","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg","contentUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/12\/dicarbon.svg"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21772#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"Carbon as a hydrogen bond acceptor: can dicarbon (C2) act in this manner?"}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa's Blog","description":"Chemistry with a twist","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Person","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281","name":"Henry Rzepa","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g370be3a7397865e4fd161aefeb0a5a85","url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","caption":"Henry Rzepa"},"description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.","sameAs":["https:\/\/orcid.org\/0000-0002-8635-8390"],"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?author=1"}]}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pDef7-5Fa","jetpack-related-posts":[{"id":10733,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733","url_meta":{"origin":21772,"position":0},"title":"Is dicarbon (C2) a molecule of chemical interest?","author":"Henry Rzepa","date":"July 3, 2013","format":false,"excerpt":"C2\u00a0(dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion,,,. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly\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":"Click for 3D","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/07\/LaOsC1.jpeg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":21798,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21798","url_meta":{"origin":21772,"position":1},"title":"Can a carbon radical act as a hydrogen bond acceptor?","author":"Henry Rzepa","date":"December 28, 2019","format":false,"excerpt":"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\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\/2019\/12\/CH-1024x940.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":10839,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10839","url_meta":{"origin":21772,"position":2},"title":"Hexacoordinate hydrogen.","author":"Henry Rzepa","date":"July 8, 2013","format":false,"excerpt":"A feature of a blog which is quite different from a journal article is how rapidly a topic might evolve.\u00a0Thus I started a few days ago with the theme of dicarbon (C2), identifying a metal carbide that showed C2 as a ligand, but which also entrapped a single carbon in\u2026","rel":"","context":"In "Hypervalency"","block_context":{"text":"Hypervalency","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=7"},"img":{"alt_text":"Click for 3D.","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/07\/6-H.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":21726,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21726","url_meta":{"origin":21772,"position":3},"title":"Hydrogen bonds: carbon as an acceptor rather than as a donor?","author":"Henry Rzepa","date":"December 23, 2019","format":false,"excerpt":"A hydrogen bond donor is considered as an electronegative element carrying a hydrogen that is accepted by an atom carrying a lone pair of electrons, as in X:...H-Y where X: is the acceptor and H-Y the donor. 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":21772,"position":4},"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":22270,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=22270","url_meta":{"origin":21772,"position":5},"title":"Discussion of (the) Room-temperature chemical synthesis of dicarbon – open and transparent science.","author":"Henry Rzepa","date":"May 6, 2020","format":false,"excerpt":"A little more than a year ago, a ChemRxiv pre-print appeared bearing the title referenced in this post, which immediately piqued my curiosity. The report presented persuasive evidence, in the form of trapping experiments, that dicarbon or C2 had been formed by the following chemical synthesis. Here I describe some\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":"","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\/21772","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=21772"}],"version-history":[{"count":20,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/21772\/revisions"}],"predecessor-version":[{"id":21845,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/21772\/revisions\/21845"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=21772"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=21772"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=21772"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=21772"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}