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

Robert Sung, Kuang-Sen Sung

Research output: Contribution to journalArticle

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 1

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Oxygen
aqueous solutions
rings
oxygen
Dimethyl Sulfoxide
acetonitrile
induction
Gases
vapor phases
Solvation
Hydrides
hydrides
Density functional theory
solvation
affinity
Thermodynamic stability
Ions
density functional theory
thermodynamics
Water

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry

Cite this

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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.",
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Insights into unusual stability of 5-membered-ring endocyclic benzyl carbocations in aqueous solution. / Sung, Robert; Sung, Kuang-Sen.

In: Journal of Physical Organic Chemistry, Vol. 31, No. 10, e3863, 01.10.2018.

Research output: Contribution to journalArticle

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