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Issue 6, 2001
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Theoretical studies on thiocarbonyl group transfer reactions

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Abstract

The gas-phase thiocarbonyl transfer reactions X  + RC([double bond, length half m-dash]S)Z ⇌ RC([double bond, length half m-dash]S)X + Z have been investigated with X, Z = Cl, Br and R = H, CH3 at the MP2 and G2(+) levels using the MP2/6-311+G** optimized geometries. The thiocarbonyl transfers proceed by a stepwise mechanism through a triple-well potential energy surface involving a tetrahedral intermediate, T. The strong proclivity toward the stepwise path is caused mainly by the low-lying πC[double bond, length half m-dash]S* level coupled with the high energy σC–Z* orbital. The reaction barriers, ΔG, are higher than the corresponding values for the carbonyl transfers, excepting for the X = Z = Cl case at the G2(+) level. The major factors for these elevated barriers, despite the low deformation energies (ΔEdef), are lower proximate σ–σ* charge transfer energies (δΔEσ–σ*(2)) and the relatively high electrostatic repulsion (ΔEes > 0) in the transition state due to the highly polarized structure with a large negative charge on the S atom. The occurrence of a well-defined intermediate, T, in the reaction coordinate leads to a relatively early transition state with a low degree of bond making and breaking in the transition state.

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Article information


Submitted
18 Dec 2000
Accepted
28 Feb 2001
First published
30 Apr 2001

New J. Chem., 2001,25, 859-863
Article type
Paper

Theoretical studies on thiocarbonyl group transfer reactions

C. K. Sohn, E. K. Ma, C. K. Kim, H. W. Lee and I. Lee, New J. Chem., 2001, 25, 859
DOI: 10.1039/B010202O

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