Thermochemical Properties Enthalpy, Entropy, and Heat Capacity of C1–C4 Fluorinated Hydrocarbons: Fluorocarbon Group Additivity

Abstract

Enthalpies of formation for 14 C2–C4 fluorinated hydrocarbons were calculated with nine popular ab initio and density functional theory methods: B3LYP, CBS-QB3, CBS-APNO, M06, M06-2X, ωB97X, G4, G4(MP2)-6X, and W1U via several series of isodesmic reactions. The recommended ideal gas phase ΔHf298° (kcal mol(–1)) values calculated in this study are the following: −65.4 for CH3CH2F; −70.2 for CH3CH2CH2F; −75.3 for CH3CHFCH3; −75.2 for CH3CH2CH2CH2F; −80.3 for CH3CHFCH2CH3; −108.1 for CH2F2; −120.9 for CH3CHF2; −125.8 for CH3CH2CHF2; −133.3 for CH3CF2CH3; −166.7 for CHF3; −180.5 for CH3CF3; −185.5 for CH3CH2CF3; −223.2 for CF4; and −85.8 for (CH3)3CF. Entropies (S298° in cal mol(–1) K(–1)) were estimated using B3LYP/6-31+G(d,p) computed frequencies and geometries. Rotational barriers were determined and hindered internal rotational contributions for S298°, and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation, with direct integration over energy levels of the intramolecular rotation potential energy curve. Thermochemical properties for the fluorinated carbon groups C/C/F/H2, C/C2/F/H, C/C/F2/H, C/C2/F2, and C/C/F3 were derived from the above target fluorocarbons. Previously published enthalpies and groups for 1,2-difluoroethane, 1,1,2-trifluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,1,2,2-pentafluoroethane, 2-fluoro-2-methylpropane that were previously determined via work reaction schemes are revised using updated reference species values. Standard deviations are compared for the calculation methods.

Thermochemistry and Kinetic Analysis of the Unimolecular Oxiranyl Radical Dissociation Reaction: A Theoretical Study

“…In a previous study, we tested B3LYP, M06, M06‐2X, ωB97X, G4, CBS‐QB3, CBS‐APNO, W1U by using work reactions for fluorinated hydrocarbons and showed that the calculations were in close agreement and had good accuracy. The B3LYP method, which combines the three parameter Becke exchange functional, B3, with the Lee–Yang–Parr (LYP) correlation functional, has been widely used for stable molecules, transition states, and radicals.…”

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH, and radicals

“…The uncertainty of a target molecule enthalpy depends on the uncertainty of work reaction calculation method, the uncertainty of reference species, and the number of isodesmic reactions . The calculation of uncertainty has been described in several previous studies . The calculated uncertainties listed in Table 2 are based on the CBS‐QB3 level calculation results of the targeted species, and the uncertainties of the reference species.…”

“…The Benson group additivity method has been widely used for the estimation of thermodynamic properties of hydrocarbons and oxygenated hydrocarbons due to its good relative accuracy and straightforward application . Results from the group additivity method for the species where groups were available in the literature are listed for comparison.…”

“…The enthalpy and entropy at 298 K and heat capacities values for CH 3 SCH 2 CH 3 can be calculated using group additivity on the following basis : (CH 3 SCH 2 CH 3 ) = (C/H3/S) + (S/C2) + (C/C/H2/S) + (C/C/H3) …”

“…All potential curves of rotational barrier versus dihedral angle were fit by a cosine curve. In this work, Rotator employs a 10‐parameter Fourier series expansion to represent the energy versus rotation dihedral angles in following form: The values of a i and b j are calculated to provide the minima and maxima of the torsional potentials with allowance for a shift of the theoretical extreme angular positions . Internal rotor torsion frequencies were omitted from the SMCPS frequency sets, and internal rotor contributions were added separately.…”