Kinetics of the hydrogen abstraction reactions of 1,1-and 1,2-difluoroethane with hydroxyl radical:: An ab initio study

The hydrogen abstraction reactions of 1,1- and 1,2-difluoroethane with the OH radical have been investigated by the nb initio molecular orbital theory The geometries of the reactants, products, and transition states have been optimized at the (U)MP2=full level of theory in conjunction with 6-311G(d,p) basis functions. Single-point (U)MP2=full with larger basis set, such as 6-311G(3d,2p), and QCISD(T)=full/6-311G(d,p) calculations have also been carried out to observe the effects of basis sets utilized and higher order electron correlation Three and four reaction channels have been identified for 1,1- and 1,2-difluoroethane, respectively. In the case of 1,1-difluoroethane, hydrogen abstraction from the alpha-carbon has been found to be easier than that from the B-carbon. The barriers of the four reaction channels for 1,2-difluoroethane are close to each other. Weak hydrogen bonding interactions have been observed between hydroxyl hydrogen and a fluorine atom in the transition states. Rate constants for the reactions of 1,1- and 1,2-difluoroethane with the OH radical have been calculated using the standard transition state theory and found to be in good agreement with the experimental results. (C) 2000 John Wiley & Sons, Inc.