Theoretical Studies on the Mechanisms and Dynamics of OH Radicals with CH₂FCF₂OCHF₂ and CH₂FOCH₂F

Abstract

The mechanisms and dynamics studies of the multichannel reactions of CH(2)FCF(2)OCHF(2) + OH (R1) and CH(2)FOCH(2)F + OH (R2) have been carried out theoretically. Three hydrogen abstraction channels and two displacement processes are found for reaction R1, whereas there are two hydrogen abstraction channels and one displacement process for reaction R2. The minimum energy paths are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the BMC-QCISD level of theory. By means of canonical variational transition state theory with small-curvature tunneling correction, the rate constants of reactions R1 and R2 are obtained over the temperature range of 220-2000 K. The rate constants are in good agreement with the experimental data for reaction R1 and estimated data for reaction R2. The Arrhenius expression k(1) = 1.62 x 10(-20) T(2.75) exp(-1011/T) for reaction R1 and k(2) = 3.40 x 10(-21) T(3.04) exp(-384/T) for reaction R2 over 220-2000 K are obtained. Furthermore, to further reveal the thermodynamics properties, the enthalpies of formation of reactants CH(2)FCF(2)OCHF(2), CH(2)FOCH(2)F, and the product radicals CHFCF(2)OCHF(2), CH(2)FCF(2)OCF(2), and CHFOCH(2)F are calculated by using isodesmic reactions.

Theoretical investigation of the mechanisms and dynamics of the reaction CHF2OCF2CHFCl+Cl

“…The difference in values may result from the OH radical and the -CHF 2 CF 2 , −OCHF 2 , which is different from us. Beyond that, the reaction CH 2 CF 2 OCHF 2 with OH radicals by Song et al [37] also come to a similar situation with our results in MEPs. At the same time, the reaction R1 is endothermic by 0.2 kcal/mol, while reaction R2 is endothermal by 4.8 kcal/mol, which indicates that reaction R1 is more favorable than reaction R2 in thermodynamics.…”

“…So the reaction R1 and R2 both proceed via indirect mechanisms. The indirect mechanisms could also be found in other articles that some halogen ethers reaction with Cl atom and OH radicals [37][38][39][40][41]. The energy of complex 1ER is 0.9 kcal/mol and complex 2ER is 0.7 kcal/mol lower than that of reactants.…”

“…This result will be proved again in the content of the kinetics. Table 2 [12,37,41]. Through the isodesmic reactions R3a-R5c, in which the number and the type of the bonds are conserved, we estimate the ΔH f,298 θ values of the above species in Table 3.…”

Kinetics and mechanism of gas-phase reaction of CF3OCH2CH3 (HFE-263) with the OH radical — a theoretical study

“…Such a case has also been shown to prevail in the case of CH 2 FCF 2 OCHF 2 and CH 2 FOCH 2 F OH radical attack during H-atom abstarction. 11 in the case of the title molecule, hydrogen may be abstracted from two different sites either from -CH 2 or from -CH 3 . The possibility of abstraction of hydrogen from -CH 3 group is dependent on the orientation of the hydrogen atoms.…”

Computational studies on the thermal decomposition of the CH2FOCHFO radical

“…The first experimental study reported in the literature is from Goto et al [18], who measured the rate constant of Cl atom reaction with CH 2 FOCH 2 F at 700 Torr and 298 K using the Smog Chamber/Fourier Transform Infra Red (FTIR) technique. Chandra et al [19] proposed a semi-empirical procedure for the estimation of the rate constant that yielded a value of 4.7 × 10 −14 cm 3 molecule −1 s −1 at 298 K for the reaction of OH radicals with CH 2 FOCH 2 F. Very recently, Song et al [20] have performed dynamic studies on the multi-channel reactions of OH radicals with CH 2 FOCH 2 F and concluded that H atom abstraction from the CH 2 F group is the main reaction channel and the displacement reactions are negligible. Christensen et al [21] studied the degradation pathways of a hydrofluoroether, CF 3 OCH 3 (HFE143a), using the Smog Chamber/FTIR technique and concluded that the haloalkoxy radical (CF 3 OCH 2 O) produced from HFE-143a degraded primarily by the reaction with O 2 in the atmosphere.…”