Why are vinyl cations sluggish electrophiles?

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dc.contributor.author Byrne, Peter A.
dc.contributor.author Kobayashi, Shinjiro
dc.contributor.author Würthwein, Ernst-Ulrich
dc.contributor.author Ammer, Johannes
dc.contributor.author Mayr, Herbert
dc.date.accessioned 2019-04-03T13:47:21Z
dc.date.available 2019-04-03T13:47:21Z
dc.date.issued 2017-01-01
dc.identifier.citation Byrne, P. A., Kobayashi, S., Würthwein, E.-U., Ammer, J. and Mayr, H. (2017) 'Why Are Vinyl Cations Sluggish Electrophiles?', Journal of the American Chemical Society, 139(4), pp. 1499-1511. doi: 10.1021/jacs.6b10889 en
dc.identifier.volume 139 en
dc.identifier.startpage 1499 en
dc.identifier.endpage 1511 en
dc.identifier.issn 0002-7863
dc.identifier.uri http://hdl.handle.net/10468/7701
dc.identifier.doi 10.1021/jacs.6b10889 en
dc.description.abstract The kinetics of the reactions of the vinyl cations 2 [Ph2C═C+–(4-MeO–C6H4)] and 3 [Me2C═C+–(4-MeO–C6H4)] (generated by laser flash photolysis) with diverse nucleophiles (e.g., pyrroles, halide ions, and solvents containing variable amounts of water or alcohol) have been determined photometrically. It was found that the reactivity order of the nucleophiles toward these vinyl cations is the same as that toward diarylcarbenium ions (benzhydrylium ions). However, the reaction rates of vinyl cations are affected only half as much by variation of the nucleophiles as those of the benzhydrylium ions. For that reason, the relative reactivities of vinyl cations and benzhydrylium ions depend strongly on the nature of the nucleophiles. It is shown that vinyl cations 2 and 3 react, respectively, 227 and 14 times more slowly with trifluoroethanol than the parent benzhydrylium ion (Ph)2CH+, even though in solvolysis reactions (80% aqueous ethanol at 25 °C) the vinyl bromides leading to 2 and 3 ionize much more slowly (half-lives 1.15 yrs and 33 days) than (Ph)2CH-Br (half-life 23 s). The origin of this counterintuitive phenomenon was investigated by high-level MO calculations. We report that vinyl cations are not exceptionally high energy intermediates, and that high intrinsic barriers for the sp2 ⇌ sp rehybridizations account for the general phenomenon that vinyl cations are formed slowly by solvolytic cleavage of vinyl derivatives, and are also consumed slowly by reactions with nucleophiles. en
dc.description.sponsorship Deutsche Forschungsgemeinschaft (SFB 749, Project B1); Alexander von Humboldt-Stiftung (Humboldt Foundation Research Fellowship) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher American Chemical Society, ACS en
dc.relation.uri http://pubs.acs.org/doi/abs/10.1021/jacs.6b10889
dc.rights © 2017 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/pdf/10.1021/jacs.6b10889 en
dc.subject Vinyl cations en
dc.subject Marcus theory en
dc.subject Electrophilicity en
dc.subject Nucleophilicity en
dc.subject Intrinsic barrier en
dc.subject Solvolysis en
dc.title Why are vinyl cations sluggish electrophiles? en
dc.type Article (peer-reviewed) en
dc.internal.authorcontactother Peter Byrne, Chemistry, University College Cork, Cork, Ireland. +353-21-490-3000 Email: peter.byrne@ucc.ie en
dc.internal.availability Full text available en
dc.date.updated 2019-03-26T17:09:55Z
dc.description.version Accepted Version en
dc.internal.rssid 383418208
dc.contributor.funder Deutsche Forschungsgemeinschaft en
dc.contributor.funder Alexander von Humboldt-Stiftung en
dc.description.status Peer reviewed en
dc.identifier.journaltitle Journal of the American Chemical Society en
dc.internal.copyrightchecked No
dc.internal.licenseacceptance Yes en
dc.internal.IRISemailaddress peter.byrne@ucc.ie en
dc.identifier.eissn 0002-7863

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