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.