Quantum Chemical and Chemical Kinetic Investigation on Hydrogen Abstraction Reactions of CF₃CF₂C(O)OCH₃ and CHF₂CF₂C(O)OCH₃ with OH Radicals and Fate of Haloalkoxy Radicals

Abstract

We performed extensive theoretical calculations to study the mechanisms, thermochemistry, and kinetics of hydrogen abstraction reactions of CF3CF2C­(O)­OCH3 and CHF2CF2C­(O)­OCH3 by OH radicals. Potential energy diagrams were constructed at the CCSD­(T)/cc-pVTZ//M06-2X/cc-pVTZ level of theory. Two stable conformers were observed for CHF2CF2C­(O)­OCH3 molecule. A total of eight hydrogen abstraction pathways are observed for the title reactions. Theoretical rate coefficients are calculated by the dual-level direct dynamics method using the canonical variational transition state theory with small-curvature tunneling (SCT) over the 200–1000 K temperature range. Rate coefficients are then fitted into a three-parameter-modified Arrhenius equation. The rate coefficients of the title reactions are compared with the literature values of similar species to establish a reactivity trend. It is concluded that C–H bond reactivity decreases with fluorine atom substitution. The atmospheric lifetime of CF3CF2C­(O)­OCH3 is calculated to be 1.15 years and that of CHF2CF2C­(O)­OCH3 to be 0.26 years. Global warming potentials are also calculated over 20, 100, and 500 year time horizons. We performed a mechanistic study to explore the atmospheric degradation of haloalkoxy radicals [CF3CF2C­(O)­OCH2O• and CHF2CF2C­(O)­OCH2O•], and the sole atmospheric fate of their consumption has also been reported.

Effect of formic acid on O2 + OH˙CHOH → HCOOH + HO2 reaction under tropospheric condition: kinetics of cis and trans isomers

“…11,15 Several investigations at similar levels of theory were reported in the literature and results were in very good agreement with the experimentally/theoretically measured/calculated values. 1,41–51 Therefore, we believe that the combination of M06-2X with CCSDT corrected energies provide the reasonably accurate value with the ∼1 kcal mol −1 energy error. 1,41–51 The RCCSD(T) method was used for closed-shell species and for all open-shell species the UCCSD(T) method was used.…”

“…1,41–51 Therefore, we believe that the combination of M06-2X with CCSDT corrected energies provide the reasonably accurate value with the ∼1 kcal mol −1 energy error. 1,41–51 The RCCSD(T) method was used for closed-shell species and for all open-shell species the UCCSD(T) method was used. To understand the qualitative assessment of the significance of the multi-reference wave function, the T 1 diagnostic was carried out at the CCSD(T)/6-311++G(3df,3pd) level for all the species.…”

Kinetics, Products, and Mechanisms Study of the Atmospheric Degradation of (E)-4-Methoxy-3-buten-2-one with Hydroxyl Radicals

“…As seen from Tables S1–S5, the T1 diagnostic values of closed-shell species are less than 0.02, and those of open-shell species are less than 0.044, indicating that the single-reference method is reliable for energies in chemical accuracy (within 4.2 kJ/mol) for the target reactions. It has been shown that the CCSD­(T) method is able to properly describe the values of energy in several systems. − Unless mentioned otherwise, the final energies reported below are calculated using the dual-level methodology CCSD­(T)/6-311++G­(d,p)//BH&HLYP /6-311++G­(d,p) + 0.9335 × ZPE, which is abbreviated hereafter as CCSD­(T)//BH&HLYP for the sake of brevity.…”

Theoretical Investigation on Hydrogen Abstraction Reactions of Sulfur Compounds HSX(O)H and CH3SX(O)H (X = C, S) by OH Radicals

“…The M06-2X , meta-hybrid exchange–correlation functional was used for DFT calculations. The M06-2X method is proven trustworthy for determining thermochemistry, reaction mechanisms, and rate coefficient calculations of atmospheric reactions of main-group elements. − For calculation purposes, we utilized Dunning’s augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) basis set. − …”