**************** The 9th., Lab Seminar ****************************

Date: Thu, November 26, 2009  PM 1:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Yoshiyuki Koyano

Title: Steric Retardation of SN2 Reactions in the Gas Phase and Solution
G. Vayner, K. N. Houk, W. L. Jorgensen, and John I. Brauman,
J. Am. Chem. Soc., 126, 9054 (2004)

Abstract:
 The gas-phase SN2 reactions of chloride with ethyl and neopentyl chlorides
and their α-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.

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