Fluorinated hydrocarbons are present in the atmosphere, hydrosphere and lithosphere as a result of past uses as solvents and propellants as well as past and current use as refrigerants and heat exchange fluids and in polymers. They exist in varied states from pure compounds to partially oxidized intermediates resulting from environmental driven oxidation of the molecular structures. The fundamental thermodynamic and chemical properties of the fluorocarbons and their oxygenated breakdown intermediates, is critical to understanding their lifetimes and reactivity in biological processes and in the environment. Thermochemical properties of C1 – C4 fluorinated molecules is critical for the estimation of both the thermodynamic and kinetic chemistry, which are applied into the physics, engineering, combustion, atmospheric, and environmental far-ranging areas. Calculation on the enthalpy of formation on fluoromethane at the extrapolated CCSD(T) computation level for energies via atomization reaction. Fluoromethane was considered the reference species in isodesmic reactions, the heat of formation enthalpy of formation, entropy and heat capacities(T ) of thirteen C1 to C4 hydrofluorocarbons (HFC’s) at 298K were calculated with up to nine ab initio and DFT methods: B3LYP, CBS-QB3, CBS-APNO, M06, M06-2X, ωB97X, G4, G4(MP2)-6X, and W1U. The results show very good accuracy when compared to limited experimental data and consistent trends. Adding an extra methyl group increased the heat of formation approximately 5.00 kcal/mol, while adding an extra fluorine atom decreased the enthalpy of formation approximately 57.00 kcal/mol. Entropy (in cal mol-1 K-1) and heat capacity (in cal mol-1 K-1) were achieved using B3LYP/6-31+G(d,p) determined geometries and frequencies with methods derived from statistical mechanics. The fluorinated carbon groups C/F/H3, C/C/F/H2, C/C2/F/H, C/F2/H2, C/C/F2/H, C/C2/F2, C/F3/H, C/C/F3, C/F4 are derived from the above target fluorocarbons. The bond dissociation energies of three related fluoro-peroxides were derived from the heat of formation of the above fourteen target fluorinated hydrocarbons based on the isodesmic reaction analysis.

Thermochemical properties enthalpy, entropy and heat capacity of C1-C4 fluorinated hydrocarbons and fluorocarbon group additivity

251st National Meeting (2016)

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