Theoretical study and rate constants calculation of hydrogen abstraction reactions CF3CHCl2 + F and CF3CHClF + 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.