Solvent Effects on Isotope Effects: Methyl Cation as a Model System

Philippe Wilson, Ian Williams

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

The isotopic sensitivity (CH3+ vs CD3+) of the equilibrium between the methyl cation in vacuum and in solution has been investigated. Two alternative options for describing the shape of the solute cavity within the widely used polarized continuum model for implicit solvation were compared; the UFF and UA0 methods give equilibrium isotope effects (EIEs) that vary as a function of the dielectric constant in opposite directions. The same isotope effect was also obtained as the average over 40 structures from a hybrid quantum mechanical/molecular mechanical molecular dynamics simulation for the methyl cation explicitly solvated by many water molecules; the inverse value of the EIE agrees with UFF but not UA0. The opposing trends may be satisfactorily explained in terms of the different degrees of exposure of the atomic charges to the dielectric continuum in cavities of different shapes.
Original languageEnglish
Pages (from-to)802-809
JournalJournal of Physical Chemistry B
Volume119
Issue number3
Early online date10 Jul 2014
DOIs
Publication statusPublished - 22 Jan 2015

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