Direct dynamics study of the hydrogen-abstraction reaction of 1,1,2,2,3-fluorinated propane with the hydroxyl radical.

The hydrogen abstraction reactions by a hydroxyl radical from 1,1,2,2,3-fluorinated propane (CF2HCF2CFH2) have been investigated by the dual-level direct dynamics method. Three equilibrium conformers (I, II, III) of CF2HCF2CFH2, one with Cs and two with C1 symmetries, are identified by the rotations of -CFH2 and -CF2H groups. Two transition states are located for the conformer I (Cs symmetry) + OH --> products (R1) reaction, and three distinct transition states are identified for conformers II and III (C1 symmetry) + OH --> products (R2 and R3). The optimized geometries and harmonic vibrational frequencies of all reactants, complexes, transition states, and products are calculated at the BB1K/6-31+G(d,p) level of theory. The single-point energy calculations are performed at the G3(MP2) level using the BB1K geometries. Using improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT), the rate constants for each channel are calculated over a wide temperature range of 200-2000 K. It is found that the H-abstraction reaction from the -CFH2 group is the predominant product channel for three reactions. The total rate constant is evaluated by the Boltzmann distribution function, and the agreement between theoretical and experimental values is good.