Thermochemistry of Intermediates and Products in the Oxidation Reaction of 1,1,2-Trifluoroethene via OH Radical.

Abstract

Density functional theory (DFT) and composite ab initio based calculations are performed on trifluoroethane along with intermediate radicals, parent molecules of the radicals, and products related to the reaction of hydroxyl radical with 1,1,2-trifluoroethene, as a reference for hydrofluoroolefins (HFO). Potential energy barriers for internal rotations have been computed. Calculated torsional potentials are incorporated into the determination of entropy, S°298, and heat capacities as a function of temperature, Cp(T), for each target molecule. Six isodesmic or isogyric reactions and five calculation methods are used to determine heats of formation at 298 K (ΔfH298) in kcal mol-1 of each target species. The CBS-APNO method shows the best agreement with experimental data in comparisons from 16 reference reactions on ΔrxnH of each method. The lowest configuration structures of each target species are reported. Intramolecular hydrogen bonds between the hydroxyl hydrogen atom and the fluorine atom on the adjacent carbon can stabilize molecules by up to 3 kcal mol-1. R-OH bond dissociation energies are observed to increase with the number of fluorine atoms on the carbon connected to hydroxy group. Recommended ΔfH298 values in kcal mol-1 derived from the most stable conformers are CF2(OH)CH2F (-213.0), CF2(O•)CH2F (-148.6), CF2(OH)C•FH (-162.4), CHF2CHFOH (-207.5), CHF2C•FOH (-158.3), C•F2CHFOH (-155.5), CHF2CHFO• (-150.4), CF3CH2OH (-212.5), and CF3C•HOH (-167.9).