Insights into unusual stability of 5-membered-ring endocyclic benzyl carbocations in aqueous solution

Robert Sung, Kuangsen Sung

Research output: Contribution to journalArticlepeer-review

Abstract

The acyclic o-oxygen benzyl carbocation 1, the 6-membered-ring endocyclic o-oxygen benzyl carbocation 2, and the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 were used as model compounds to get insights into the general phenomenon for the unusual stability of the 5-membered-ring endocyclic benzyl carbocations in aqueous solution. The hydride-ion affinities of 1, 2, and 3 in gas phase, acetonitrile, and DMSO were calculated and compared by the density functional theory method, and 3 isodesmic reactions were designed to confirm their thermodynamic stability. What we found is that the 5-membered-ring endocyclic o-oxygen stabilizes the benzyl carbocation 3 less than the acyclic o-oxygen stabilizes the benzyl carbocation 1 in gas phase because of ring strain and through-bond induction. However, the high solvation energies of the 5-membered-ring endocyclic o-oxygen benzyl carbocation 3 not only offset the destabilizing effects of ring strain and through-bond induction but also make it even more stable than the acyclic o-oxygen benzyl carbocation 1 in polar solvents like acetonitrile, DMSO, and water.

Original languageEnglish
Article numbere3863
JournalJournal of Physical Organic Chemistry
Volume31
Issue number10
DOIs
Publication statusPublished - 2018 Oct

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry

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