Theoretical Studies of the Reactions CF_xH_3−xCOOR+Cl and CF₃COOCH₃+OH

Abstract

The mechanism and kinetics of the reactions of CF(3)COOCH(2)CH(3), CF(2)HCOOCH(3), and CF(3)COOCH(3) with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06-2X methods with the 6-311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6-311++G(d,p) methods. Seven hydrogen-abstraction channels are found. All the rate constants, computed by a dual-level direct method with a small-curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low-temperature range. For the reaction of CF(3)COOCH(2)CH(3) +Cl, H-abstraction from the CH(2) group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200-1000 K as kT(1) =8.4×10(-20) T (2.63) exp(381.28/T), kT(2) =2.95×10(-21) T (3.13) exp(-103.21/T), kT(3) =1.25×10(-23) T (3.37) exp(791.98/T), and kT(4) =4.53×10(-22) T (3.07) exp(465.00/T).

Theoretical insight into OH- and Cl-initiated oxidation of CF3OCH(CF3)2 and CF3OCF2CF2H & fate of CF3OC(X•)(CF3)2 and CF3OCF2CF2X• radicals (X=O, O2)

“…The B3LYP method is more widely used for predicting the reliable geometries of the stationary points, and found to be accurate from the previous studies121516505152535455. Moreover, B3LYP theory is able to suppress effectively the problem of spin contamination.…”

Atom Tunneling in Chemistry

“…Hydrogen atoms are frequently found to tunnel, even at room temperature,inclassical reactions of organic chemistry. In the case of reactions of closed-shell molecules with radicals, hydrogen is abstracted if the emerging radical is more stable than the previous one.V arious reactions of small organic molecules with hydrogen atoms, [153][154][155][156] hydroperoxyl radicals, [64] chlorine atoms, [157][158][159][160] or the activation of H 2 [161] have been studied experimentally as well as computationally. These reactions are influenced by tunneling,e ven at room temperature,t hereby raising the reaction rate constants.F or Claisen rearrangements it was necessary to computationally include am odel of tunneling through ap arabolic barrier to explain the experimental 13 CK IEs, [162][163][164] and in aS wern oxidation, multidimensional tunneling had to be included in computations to reproduce the experimental results.…”

“…In the case of reactions of closed-shell molecules with radicals, hydrogen is abstracted if the emerging radical is more stable than the previous one. Various reactions of small organic molecules with hydrogen atoms, [153][154][155][156] hydroperoxyl radicals, [64] chlorine atoms, [157][158][159][160] or the activation of H 2 [161] have been studied experimentally as well as computationally. Even at room temperature these reactions are influenced by tunneling, raising the reaction rate constants.…”

Atmospheric chemistry of alkyl iodides: theoretical studies on the mechanisms and kinetics of CH3I/C2H5I + NO3reactions

“…The T 1 values of all the species in our system were smaller than 0.045, indicating that the multireference character in the CCSD(T) wave functions is not a problem. 34,35 On the basis of the initial PES information, including the optimized geometries, energies, and frequencies along the MEPs, the rate constants were calculated over the wide temperature range of 220-800 K using the canonical variational transition state theory (CVT), [36][37][38] which also involved the smallcurvature tunneling correction (SCT) 39,40 method proposed by Truhlar and co-workers. Dynamic calculations of the variational transition state theory with interpolated single-point energies (VTST-ISPE) 41 were carried out using the POLYRATE-Version 9.7 program.…”