Density functional and G2 study of the strength of the OH bond in CF3OH

The gas-phase acidity of CF3OH was calculated using density functional methods (B3LYP, B3PW91). The best value obtained, Delta H-acid(0) = 328.9 kcal mol(-1), agrees with experiment (329.8 +/- 2.0 kcal mol(-1)). This acidity was employed to determine the CF3O-H bond strength, using the same thermodynamical cycle as in the experimental work. Both methods give lower values than the experimentally derived one. Comparison of the calculated values in the thermodynamical cycle with experiment shows that the B3PW91 results are within the error bars or slightly outside them for all the reactions except the thermal decomposition of CF3OOCF3. The results suggest that the experimental O-O bond dissociation energy of CF3OOCF3 has been overestimated. Using the experimental value of the enthalpy of formation of H+, the B3PW91 O-H bond strength, 118.0 +/- 0.3 kcal/mol, agrees with the G2 value, 119.4 +/- 0.9 kcal/mol, but is still lower than the experimentally derived one, 124.7 +/- 3.6 kcal/mol. (C) 1997 Elsevier Science B.V.