Conformational stability, barriers to internal rotation, ab initio calculations and vibrational assignment for chlorodifluoroacetyl chloride

Abstract

The Raman (1900 to 10 cm−1) and infrared (1900 to 30 cm−1) spectra of chlorodifluoroacetyl chloride, CClF2CClO, in the gas and solid phases have been recorded. The Raman spectrum of the liquid, and qualitative depolarization ratios, have also been obtained. These data have been interpreted on the basis of an equilibrium between the gauche and trans conformers (chlorine atom trans to the other chlorine atom) in the gas and liquid phases. From the study of the Raman spectrum of the liquid at different temperatures, a value of 361 ± 40 cm−1 (1.03 ± 0.11 kcal mol−1) was determined for ΔH with the gauche conformer being the more stable form. A similar study of the sample dissolved in liquid xenon gave a ΔH value of 249 ± 60 cm−1 (0.71 ± 0.17 kcal mol−1), again with the gauche rotamer the more stable conformer. Therefore, the gauche conformer is the predominate rotamer in the gas and liquid and the only conformer present in the annealed solid. A complete vibrational assignment is proposed for both conformers based on infrared band contours. Raman depolarization data, group frequencies and normal coordinate calculations. Optimized geometries, conformational stabilities, unscaled and scaled vibrational frequencies and harmonic force fields are 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 with the corresponding results for some similar molecules.