{"id":23240,"date":"2021-01-20T14:34:16","date_gmt":"2021-01-20T14:34:16","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=23240"},"modified":"2021-01-21T09:04:53","modified_gmt":"2021-01-21T09:04:53","slug":"the-chemical-synthesis-of-c2-another-fascinating-twist-to-the-story","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23240","title":{"rendered":"The chemical synthesis of C2: another fascinating twist to the story."},"content":{"rendered":"
\n

Last May, I wrote an update<\/a> to the story sparked by the report of the chemical synthesis of C2<\/sub>.[1]<\/a><\/span> This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures.[2]<\/a><\/span> The chemical synthesis however was done in solution at ambient or low temperatures, a game-changer as they say. Here I give another update to this unfolding story.
\n\"\"<\/a><\/p>\n

Key to the story is the precursor labelled 11<\/b> in the scheme above and the suggestion[1]<\/a><\/span> that it is unimolecular<\/strong> decomposition of 11<\/strong>\u00a0that results in C2<\/sub>. A question that had not been posed however was whether 11<\/strong>\u00a0itself could participate in any bimolecular<\/strong> reactions and whether these could be lower in free energy than its unimolecular decomposition. That has now been addressed in a recent pre-print, DOI: 10.26434\/chemrxiv.13560260.v1<\/a>[3]<\/a><\/span> Here I will show just one of the possible bimolecular reactions investigated, that of 11<\/strong> with itself.\u00a0<\/p>\n

\"\"<\/a>\"\"<\/a>
\n<\/a>The reaction has a low barrier (\u0394G\u2021<\/sup> 15.4 kcal\/mol for a standard state of 0.044 molar, approximately the concentration the original experiments were conducted for) which means it will be very rapid at room temperatures.\u2665<\/sup><\/span> The product of this reaction can itself react with more 11<\/strong> ((\u0394G\u2021<\/sup> 16.9 kcal\/mol) and so on to form polymeric chains or clusters of carbon, eventually resulting in C60<\/sub> and other forms of carbon. Low energy barriers for a number of other possible bimolecular reactions of 11<\/strong> with species such as the chemical traps used in the original experiment are also reported,[3]<\/a><\/span> most of which are lower in free energy than that predicted for the unimolecular fragmentation of 11<\/strong>, despite the entropic penalty.<\/p>\n

So the enigma is thus: Does species 11<\/strong> truly fragment to C2<\/sub>, or are the products of this reaction really bimolecular reactions of 11<\/strong>? It does seem as if 11<\/strong> itself can have a rich and fascinating room temperature chemistry, the scope of which has only started to be explored.<\/p>\n

\n

\u2665<\/sup><\/span>The potential energy surface is unusual, in that initially two products are possible, depending on where the C4<\/sub> unit ends up attached. The potential energy valley only bifurcates into two valleys resulting in the final product at a late stage (~ IRC -5). Put another way, the initial symmetry is C2h<\/sub>, but this breaks\/bifurcates into two valleys each leading to different outcomes for the C4<\/sub> unit. This is very much like the famous potential energy surface for the dimerisation of cyclopentadiene<\/a>.<\/p>\n

References<\/h2>\n
  1. K. Miyamoto, S. Narita, Y. Masumoto, T. Hashishin, T. Osawa, M. Kimura, M. Ochiai, and M. Uchiyama, \"Room-temperature chemical synthesis of C2\", Nature Communications<\/i>, vol. 11, 2020. https:\/\/doi.org\/10.1038\/s41467-020-16025-x<\/a>\n\n<\/li>\n
  2. T.W. Schmidt, \"The Spectroscopy of C<sub>2<\/sub>: A Cosmic Beacon\", Accounts of Chemical Research<\/i>, vol. 54, pp. 481-489, 2021. https:\/\/doi.org\/10.1021\/acs.accounts.0c00703<\/a>\n\n<\/li>\n
  3. H. Rzepa, \"No Free C2 Is Involved in the DFT-Computed Mechanistic Model for the Reported Room-Temperature Chemical Synthesis of C2.\", 2021. https:\/\/doi.org\/10.26434\/chemrxiv.13560260.v1<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    Last May, I wrote an update to the story sparked by the report of the chemical synthesis of C2. This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures. The chemical synthesis however was done in solution at ambient or low temperatures, a game-changer as […]<\/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":[4],"tags":[],"ppma_author":[2661],"class_list":["post-23240","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"yoast_head":"\nThe chemical synthesis of C2: another fascinating twist to the story. - 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=23240\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The chemical synthesis of C2: another fascinating twist to the story. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Last May, I wrote an update to the story sparked by the report of the chemical synthesis of C2. 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Here I add a little to the talk given\u2026","rel":"","context":"In "Historical"","block_context":{"text":"Historical","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=565"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":21009,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=21009","url_meta":{"origin":23240,"position":3},"title":"Diatomics with eight valence-electrons: formation by radioactive decay.","author":"Henry Rzepa","date":"June 2, 2019","format":false,"excerpt":"This is a follow up to my earlier post about C\u2a78N+, itself inspired by this ChemRxiv pre-print which describes a chemical synthesis of singlet biradicaloid C2 and its proposed\u00a0identification as such by chemical trapping. First row diatomics based on the iso-electronic principle of eight valence electrons include both C\u2a78N+ and\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":[]},{"id":20933,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20933","url_meta":{"origin":23240,"position":4},"title":"Startling bonds: revisiting C\u2a78N+, via the helium bond in N\u2261C-He+.","author":"Henry Rzepa","date":"May 27, 2019","format":false,"excerpt":"Although the small diatomic molecule known as dicarbon or C2 has been known for a long time, its properties and reactivity have really only been determined\u00a0via its very high temperature generation. My interest started in 2010, when I speculatively proposed here that the related isoelectronic species C\u2a78N+ might sustain a\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":[]},{"id":10733,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733","url_meta":{"origin":23240,"position":5},"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? 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