title: Steric retardation of SN2 reactions in the gas phase and solution.
abstract: The gas-phase S(N)2 reactions of chloride with ethyl and neopentyl chlorides and their alpha-cyano derivatives have been explored with B3LYP, CBS-QB3, and PDDG/PM3 calculations. Calculations predict that the steric effect of the tert-butyl group raises the activation energy by about 6 kcal/mol relative to methyl in both cases. Solvent effects have been computed with QM/MM Monte Carlo simulations for DMSO, methanol, and water, as well as with a polarizable continuum model, CPCM. Solvents cause a large increase in the activation energies of these reactions but have a very small differential effect on the ethyl and neopentyl substrates and their cyano derivatives. The theoretical results contrast with previous conclusions that were based upon gas-phase rate measurements.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
authors.forename: Grigoriy
authors.initials: G
authors.lastname: Vayner
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.forename: William L
authors.initials: WL
authors.lastname: Jorgensen
authors.forename: John I
authors.initials: JI
authors.lastname: Brauman