Theoretical Insights into Hydrogen Abstraction Reactions of CF 3 CHFOCF 3 and CF 3 CH 2 OCF 3 by Hydroxyl Radicals

This work investigates the gas-phase reactivity of fluorinated ethers CF3CHFOCF3 and CF3CH2OCF3 toward •OH radicals, corresponding to the reactions CF3CHFOCF3 + •OH → CF3C•FOCF3 + H2O (1) and CF3CH2OCF3 + •OH → CF3C•HOCF3 + H2O (2). Geometry optimizations and harmonic vibrational frequency calculations were performed at the M06-2X/6-311++G(3df,3pd) level of theory. More accurate energy estimates were obtained via single-point calculations using the CBS-QB3//M06-2X/6-311++G(3df,3pd) composite method. The potential energy profiles derived at 0 K indicate that, for both ethers, H-abstraction reactions proceed through transition states involving the formation of pre- and postreactive complexes. Rate constants were calculated over the temperature range of 200-1000 K employing canonical transition state theory (CTST), incorporating tunneling corrections via the Eckart method. The high-pressure limit Arrhenius equations derived at the CBS-QB3//M06-2X/6-311++G(3df,3pd) level can be represented by k = C exp-(D1 - (D2/T))/T, where C = (5.9 ± 1.7) × 10-12 cm3 molecule-1 s-1, D1 = (4032 ± 1327) K, and D2 = (4.7 ± 1.1) × 105 K2 for reaction (1), and C = (1.2 ± 0.2) × 10-11 cm3 molecule-1 s-1, D1 = (2921 ± 1168) K, and D2 = (2.9 ± 0.8) × 105 K2 for reaction (2). Additionally, atmospheric lifetimes of the studied ethers were estimated and discussed.