{"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":"2021-01-20T14:34:16","modified_gmt":"2021-01-20T14:34:16","slug":"the-chemical-synthesis-of-c2-another-fascinating-twist-to-the-story","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2021\/01\/20\/the-chemical-synthesis-of-c2-another-fascinating-twist-to-the-story\/","title":{"rendered":"The chemical synthesis of C2: another fascinating twist to the story."},"content":{"rendered":"

Last May, I wrote an update<\/a> to the story sparked by the report of the chemical synthesis of C2<\/sub>.[cite]10.1038\/s41467-020-16025-x[\/cite] This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures.[cite]10.1021\/acs.accounts.0c00703[\/cite] 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[cite]10.1038\/s41467-020-16025-x[\/cite] 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>[cite]10.26434\/chemrxiv.13560260.v1[\/cite] 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,[cite]10.26434\/chemrxiv.13560260.v1[\/cite] 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","protected":false},"excerpt":{"rendered":"

Last May, I wrote an update to the story sparked by the report of the chemical synthesis of C2.[cite]10.1038\/s41467-020-16025-x[\/cite] This species has a long history of spectroscopic observation in the gas phase, resulting from its generation at high temperatures.[cite]10.1021\/acs.accounts.0c00703[\/cite] The chemical synthesis however was done in solution at ambient or low temperatures, a game-changer as […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-23240","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/23240","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=23240"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/23240\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=23240"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=23240"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=23240"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}