Web Release Date: June 11,
Ab Initio Electronic Structure Study of One-Electron Reduction of Polychlorinated Ethylenes
Fundamental Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352
OGI School of Science & Engineering, Oregon Health & Science University, 20000 NW Walker Road, Beaverton, Oregon 97006-8921
Received: December 8, 2004
In Final Form: April 1, 2005
Abstract:
Polychlorethylene radicals, anions, and radical anions are potential intermediates in the reduction of
polychlorinated ethylenes (C2Cl4, C2HCl3, trans-C2H2Cl2, cis-C2H2Cl2, 1,1-C2H2Cl2, C2H3Cl). Ab initio
electronic structure methods were used to calculate the thermochemical properties, 
(298.15 K),
S
(298.15 K,1 bar), and 
GS(298.15 K, 1 bar) of 37 different polychloroethylenyl radicals, anions, and radical
anion complexes, C2HyCl3-y
, C2HyCl3-y-, and C2HyCl4-y- for y = 0-3, for the purpose of characterizing
reduction mechanisms of polychlorinated ethylenes. In this study, 8 radicals, 7 anions, and 22 radical anions
were found to have stable structures, i.e., minima on the potential energy surfaces. This multitude of isomers
for C2HyCl4-y- radical anion complexes are 
*, 
*, and -H···Cl- structures. Several stable * radical anionic
structures were obtained for the first time through the use of restricted open-shell theories. On the basis of
the calculated thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase)
for several mechanisms of the first electron reduction of the polychlorinated ethylenes were determined. In
almost all of the gas-phase reactions, the thermodynamically most favorable pathways involve -H···Cl-
complexes of the C2HyCl4-y- radical anion, in which a chloride ion is loosely bound to a hydrogen of a
C2HxCl2-x radical. The exception is for C2Cl4, in which the most favorable anionic structure is a loose *
radical anion complex, with a nearly iso-energetic * radical anion. Solvation significantly changes the product
energetics with the thermodynamically most favorable pathway leading to C2HyCl3-y + Cl-. The results
suggest that a higher degree of chlorination favors reduction, and that reduction pathways involving the
C2HyCl3-y- anions are high energy pathways.
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