An ab initio investigation of the reactions of 1,1-and 1,2-dichloroethane with hydroxyl radical

The hydrogen abstraction reactions by OH radical from 1,1-dichioroethane an d 1,2-dichloroethane have been investigated by ab initio molecular orbital theory. Optimized geometries and harmonic vibrational frequencies have been calculated for all reactants, transition structures, and products at the ( U)HF/6-311G(d,p) and (U)MP2=full/6-311G(d,p) levels of theory. Single point QCISD(T)/6-311G(d,p)//(U)MP2=full/6-311G(d,p) calculations have also been carried out for the inclusion of higher order electron correlation. Three d istinct transition structures have been located for the H3C-CHCl2 + OH reac tion (one for alpha-abstraction and two for beta-abstraction). Four transit ion structures have been located for the reaction ClH2C-CH2Cl + OH. The cal culated barrier heights, reaction enthalpies, and change in entropy are fou nd to be in good agreement with available experimental values. In addition, the rate constants calculated by using the transition state theory are fou nd to be in good agreement with the experimental results. Non-Arrhenius beh avior of the rate constants arises from the tunneling effects and availabil ity of multiple reaction channels.