Why are vinyl cations sluggish electrophiles?

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dc.contributor.authorByrne, Peter A.
dc.contributor.authorKobayashi, Shinjiro
dc.contributor.authorWürthwein, Ernst-Ulrich
dc.contributor.authorAmmer, Johannes
dc.contributor.authorMayr, Herbert
dc.contributor.funderDeutsche Forschungsgemeinschaften
dc.contributor.funderAlexander von Humboldt-Stiftungen
dc.date.accessioned2019-04-03T13:47:21Z
dc.date.available2019-04-03T13:47:21Z
dc.date.issued2017-01-01
dc.date.updated2019-03-26T17:09:55Z
dc.description.abstractThe 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.sponsorshipDeutsche Forschungsgemeinschaft (SFB 749, Project B1); Alexander von Humboldt-Stiftung (Humboldt Foundation Research Fellowship)en
dc.description.statusPeer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationByrne, 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.6b10889en
dc.identifier.doi10.1021/jacs.6b10889en
dc.identifier.eissn0002-7863
dc.identifier.endpage1511en
dc.identifier.issn0002-7863
dc.identifier.journaltitleJournal of the American Chemical Societyen
dc.identifier.startpage1499en
dc.identifier.urihttps://hdl.handle.net/10468/7701
dc.identifier.volume139en
dc.language.isoenen
dc.publisherAmerican Chemical Society, ACSen
dc.relation.urihttp://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.6b10889en
dc.subjectVinyl cationsen
dc.subjectMarcus theoryen
dc.subjectElectrophilicityen
dc.subjectNucleophilicityen
dc.subjectIntrinsic barrieren
dc.subjectSolvolysisen
dc.titleWhy are vinyl cations sluggish electrophiles?en
dc.typeArticle (peer-reviewed)en
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