Theoretical study and rate constants calculation of hydrogen abstraction reactions CF3CHCl2Â +Â F and CF3CHClFÂ +Â F

The hydrogen abstraction reactions of CF3CHCl2 + F (R1) and CF3CHClF + F (R2) are investigated by dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the B3LYP/6-311G(d,p) and MP2/6-311G(d,p) levels. Higher-level energies are obtained at the G3(MP2) method using the B3LYP and MP2-optimized geometries, respectively. Complexes with energies lower than those of the reactants are located at the entrance of these two reactions at the B3LYP level, respectively. Using the variational transition-state theory (VTST) with the inclusion of the small-curvature tunneling correction, the rate constants are calculated over a wide temperature range of 200-2000 K. The agreement between theoretical and experimental rate constants is good. In addition, the effect of fluorine substitution on reactivity of the C-H bond is discussed. Our calculations show that the fluorine substitution deactivates the C-H bond reactivity.