Heats of Formation of Simple Perfluorinated Carbon Compounds

The heats of formation of CF 3, its cation and anion, CF 4, C 2 F 4, and:CFCF 3 have been calculated at high levels of ab initio molecular orbital theory. Geometries and frequencies were determined, in general, with second-order perturbation theory. Total energies based on coupled cluster calculations with perturbative triples were determined with basis sets up through augmented quadruple-ζ in quality and were subsequently extrapolated to the complete one-particle basis set limit, so as to further reduce the basis set truncation error. Due to its importance as a standard, CF 4 was studied with even larger basis sets. Additional improvements in the atomization energy were achieved by applying corrections due to core/valence correlation, scalar relativistic, and atomic spin−orbit effects. Zero-point energies were based on the experimental fundamentals, when available, and harmonic frequencies obtained from MP2/cc-pVTZ calculations. Missing frequencies for:CFCF 3 were calculated at the MP2/DZP level. The calculated heats of formation (kcal/mol) are as follows: Δ H f (CF 4 ) = −221.8 ± 1.1 vs −221.6 ± 0.3 (expt); Δ H f (CF 3 ) = −111.9 ± 1.0 vs −111.7 ± 1.0 (expt); Δ H f (CF 3 + ) = 98.0 ± 1.2 vs 99.8 ± 2.8 (expt); Δ H f (CF 3 - ) = −151.9 ± 0.7 vs −154.9 ± 1.0 (expt); Δ H f (C 2 F 4 ) = −159.8 ± 1.5 vs −156.6 ± 0.7 (expt); and Δ H f (:CFCF 3 ) = −122.6 ± 1.5, all at 0 K. These values are used to calculate a variety of bond energies and molecular energetics.