Dual-level direct dynamics studies on the hydrogen abstraction reactions of fluorine atoms with CF3CH2X(X=F,Cl)

The kinetic properties of the hydrogen abstraction reactions of CF₃CH₂F + F → CF₃CHF + HF (R1) and CF₃CH₂Cl + F → CF₃CHCl + HF (R2) have been studied by dual-level direct dynamics method. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path (MEP) were obtained at the B3LYP/6-311 + G(2d,2p) level. Two complexes with energies less than that of the reactants were located in the reactant side of each reaction. The energy profiles were further refined with the interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. Using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) method, the rate constants were evaluated over a wide temperature range of 200–2,000 K. Our calculations have shown that C–H bond activity decreases when one hydrogen atom of CF₃CH₃ is substituted by a fluorine atom, than when substituted with a chlorine atom. This is in good agreement with the experimental results.