Theoretical study of the internal elimination reactions of xanthate precursors

Abstract

The gas-phase internal elimination (E-i) reaction of ethyl xanthate (CH3-CH2-S-CS-O-CH3) has been investigated by means of Hartree-Fock, second-order Moller-Plesset, and density functional theory (DFT) using the Becke three-parameter Lee-Yang-Parr (B3LYP) functional and the modified Perdew-Wang one-parameter model for kinetics (MPW1K). Considerable differences between the ground- and transition-state geometries and the calculated activation energies are observed from one approach to the other, which justifies first a careful calibration of the methods against the results of benchmark CCSD(T) calculations. Compared with these, DFT calculations along with the MPW1K functional are found to be an appropriate choice for describing the E-i reaction of xanthate precursors. The precursor conformation and the transition states involved in the internal conversion of xanthate precursors of cyano derivatives of ethylene, and of cis- and trans-stilbene, are then characterized in detail by means of this functional. (C) 2003 Wiley Periodicals, Inc.