The transition state energy for Cl, molecular elimination from 1,2-dichloroethane is computed at compostite CBS-Q (based on B3LYP/6-31++G(d) optimized structure) and G3MP2 (based on MP2/6-31++G(d) optimized structure) levels of theory. Forward rate constants are calculated as 4.25E11T(0.826).exp(-93.4 kcal mol(-1)/RT) and 7.62E10T(0.892).exp(-98.5 kcal mol(-1) /RT)s(-1), respectively for these two methods, Intrinsic reaction coordinate (IRC) analysis is performed to verify the transition state structures. While the overall, elimination of Cl, plus olefin formation has a relative low DeltaH(rxh): the reaction with these barriers is evaluated to be not important in thermal reactions of chlorocarbons. (C) 2002 Published by Elsevier Science B.V.