CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, AB-INITIO CALCULATIONS, AND VIBRATIONAL ASSIGNMENT FOR FLUORODICHLOROACETYL CHLORIDE

The Raman (2000 to 10 cm(-1)) and infrared (2000 to 30 cm(-1)) spectra of both the gaseous and solid phases of fluorodichloroacetyl chloride , CCl2FCClO, have been recorded. In addition, the Raman spectrum of th e liquid; along with qualitative depolarization ratios, has been obtai ned. These data have been interpreted on the basis of an equilibrium b etween the gauche and trans conformers (fluorine atom trans to the chl orine atom of the CClO top) in the gaseous and liquid phases. From the study of the Raman spectrum of the liquid at different temperatures, a value of 110 + 24 cm(-1) (316 +/- 68 cal mol(-1)) was determined for Delta H with the trans conformer being the more stable form. A simila r study of the sample dissolved in liquid xenon gave a Delta H value o f 177 +/- 14 cm(-1) (506 +/- 40 cal mol(-1)), again with the trans rot amer the more stable conformer. Therefore, the trans conformer is the predominate rotamer in the gas and liquid, and the only conformer pres ent in the annealed solid. A complete vibrational assignment is propos ed for both conformers based on infrared band contours, Raman depolari zation data, group frequencies, and normal coordinate calculations. Op timized geometries, conformational stabilities, unsealed and scaled vi brational frequencies, and harmonic force fields are neo reported for both conformers from ab initio calculations utilizing the RHF/3-21G, RHF/6-31G and/or MP2/6-31G* basis sets. These results are compared wi th the corresponding results for some similar molecules.