Thermochemistry of Gas-Phase Equilibrium CF₃CH₃ + I₂ = CF₃CH₂I + HI. The Carbon-Hydrogen Bond Dissociation Energy in 1,1,1-Trifluoroethane and the Heat of Formation of the 2,2,2-Trifluoroethyl Radical

Abstract

35)The experimental results with w h i i we are primarily interested are the values of D/S for c-C&T and c-C&T measured for samples simultaneously containing c-C4H8 and c-CP8.4 In these mixtwes both mdecules are e x w to the same tritlum atom flux and the DIS values have been measured for equivalent experimental conditions. However, the D/S values for C-CI H~T in pwe c-C4Hs3 and in C-CIH~-C-C& mixtures" are the same, M i t i n g the T atom flux and the deactivation processes of c-C"!+T do not differ appreciably in the two systems. (36) The distance of the H or D atom from the cyclobutane center of mass is (37) T. Valencich and D. L. Bunker, ref 29, find at a T-atom energy of 200 kcallmol Walden inversion substlutions resuits in the ejected atoms canyirig an average fractiin of 0.20 of the incident energy with a largest fraction of 0.48. For substiution with retention the fractions are 0.25 and 0.62, respectively. These fractions change very little over a 500 kcal/mol range of T-atom energies: e.& for retained substitutions the smallest average fraction of energy carried by the ejected atom is at 130 kcallmol and equals 0.22, with a largest average fraction at 400 kcal/md equal to 0.36. (38) P. J. Kunb. E. M. Nemeth. J. C. Polanyi, and W. H. Wong, J. Chem. phys., 52, 4654 (1970); f que+ 0.57, 0.26, 0.42, and 0.38 at 46, 92, 138, and 277 kcal/mol, respectively. The equilibrium constants for the gas-phase reaction CF3CH3 + I2 = CFsCH2I+ HI have been determined spectroscopically over the temperature range 730-775 K. The entropy of CF3CHzI was estimated and combined with known entropies for the other reagents and the experimental equilibrium constants to yield Mr0(750) = 16.0 f 0.5 and f l r 0 ( 2 9 8 ) = 15.3 f 0.5 kcal mol-'. This result yields DH02g8(CF3CHpH) = 106.7 f 1.1 kcal mol-', indicating a marked strengthening of the C(sp3)-H bond dissociation energy with 6fluorine substitution. This value for the C-H bond dissociation energy was combined with known thermochemistry to yield the heat of formation of the 2,2,2-trifluoroethyl radical, .Wfo(CF&H2, g, 298) = -123.6 f 1.2 kcal mol-'.

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

“…We calculate the reaction enthalpies of R6–R14 and combine them with the known enthalpies of formation of the reference compounds involved in these reactions. (CF 3 CF 3 : −321.20 kcal/mol32; CH 4 : −17.89 kcal/mol32; CH 3 F: −55.999 kcal/mol32; CH 2 F 2 : −107.71 kcal/mol32; CH 3 : 34.82 kcal/mol32; CF 3 CH 3 : −178.94 ± 0.76 kcal/mol33; CH 3 OCH 3 : −43.99 ± 0.12 kcal/mol34; CH 3 OH: −48.0 kcal/mol35; H 2 O: −57.799 kcal/mol36; CH 2 O: −27.701 kcal/mol36; HCO: 10.40 kcal/mol36) to evaluate the required enthalpies of formation. All of the geometrical parameters of the species in the isodesmic reactions are calculated at the B3LYP/6‐311G(d,p) level, and energies of the species are refined at the G3(MP2) level.…”

Theoretical Study of the Reactions of CF3OCHF2 with the Hydroxyl Radical and the Chlorine Atom

“…The standard enthalpies of formation of the title ether and the corresponding radical are estimated by the dual-level approach from a consideration of the applicable working chemical reactions, where the only unknown quantity is the enthalpy of formation in question. The group-balanced isodesmic Reactions (5) and (6) The derivation is made according to the following steps: 1) the geometrical parameters and harmonic vibrational frequencies for all the reactants and products involved in Reactions (5) and (6) are calculated at the B3LYP/6-311G(d,p) level; 2) three theoretical approaches, G3(MP2), G2M, and MP2/6-311 + G(3df,2p), are carried out to correct the total electronic energies of all the species in the two reactions; 3) using standard methods of statistical thermodynamics, a heat correction is applied to obtain the reaction enthalpy at 298 K; and finally, 4) these theoretical reaction enthalpies at 298 K are combined with the known heats of formation of the reference compounds in Reactions (5) and (6) (CH 3 CH 3 À20.01 AE 0.07, [30] CH 4 À17.91, [31] CF 3 CH 3 À179.1 AE 0.8, [32] CH 3 OCH 3 À44.0 AE 0.1, [33] [31] HCl À22.08 kcal mol À1 [31] ), the standard reaction enthalpies of Reactions (1) and (2) could be estimated to be À11.7 kcal mol À1 for Reaction (1) and 3.9 kcal mol À1 for reaction (2), within the error limit of 1.9 kcal higher than that of Reaction (1). Thus, the hydrogen abstraction channel is more favorable and the displacement processes are negligible for the title ether with the OH radical reaction system.…”

Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with Cl

“…Because of the lack of the knowledge of the enthalpies of formation (Δ H ) of the species involved in the title reaction, here we employ isodemic reactions R3–R5 and a relatively cheap theoretical method to predict them. The enthalpies of formation of the species are evaluated by using the known heats of formation involved in the reactions (CH 3 : 34.82 kcal/mol 37, CH 4 : −17.89 kcal/mol 37, CH 2 F 2 : −107.71 kcal/mol 37; CHF 3 : −166.60 kcal/mol 37, CF 3 : −112.40 kcal/mol 37, CF 3 CF 3 : −321.20 kcal/mol 37, CF 3 CH 3 : −178.94 ± 0.76 kcal/mol 38, and CH 3 OCH 3 : −43.99 ± 0.12 kcal/mol 39). Table IV lists the calculated results and the available literature data 40.…”