One-electron-transfer reactions of polychlorinated ethylenes: Concerted and stepwise cleavages

Reaction barriers were calculated by using ab initio electronic structure mediods for the reductive dechlorination of the polychlorinated ethylenes: C₂Cl₄, C₂HCl₃, trans-1,2-C ₂H₂Cl₂, cis-1,2-C₂H ₂Cl₂, 1,1-C₂H₂Cl₂ and C₂H₃-Cl. Concerted and stepwise cleavages of R-Cl bonds were considered. Stepwise cleavages yielded lower activation barriers than concerted cleavages for the reduction of C₂CU, C₂HCl ₃, and trans-1,2-C₂H₂Cl₂ for strong reducing agents. However, for typical ranges of reducing strength concerted cleavages were found to be favored. Both gas-phase and aqueous-phase calculations predicted C₂Cl₄ to have the lowest reaction barrier. Additionally, the reduction of C₂HCl₃ was predicted to show selectivity toward formation of cis-1,2-C₂HCl ₂· over the formation of trans-1,2-C₂HCl ₂·', and 1,1-C₂HCl₂· radicals.