Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignments for chlorodifuoroacetyl fluoride

The Raman spectra (2000-10 cm(-1)) of chlorodifluoroacetyl fluoride, CClF2CFO, in the liquid phase with qualitative depolarization ratios and the crystalline solid were recorded. The infrared spectra (2000-30 cm(-1)) of the vapor and solid phases were also obtained and additional spectra of the sample dissolved in liquid xenon were recorded at different temperatures between -100 and -55 degrees C. The data were interpreted in terms of an equilibrium between a gauche conformer which is predominant in the vapor and liquid phases and an anti (the chlorine atom is trans to the fluorine atom on the CFO moiety) conformer with only the gauche conformer present in the crystalline solid. From infrared band intensities of chlorodifluoroacetyl fluoride in xenon in the temperature range 173-213 K, taking into account intensity differences predicted from ab initio calculations, a value of Delta H = 422 +/- 40 cm(-1) is estimated with the gauche conformer being the more stable form. Optimized geometries and conformational stabilities were derived from ab initio: calculations at the levels of RHF/6-31G*, MP2/6-31G* and MP2/6-311 + G** with all of the calculations predicting the gauche rotamer to be the most stable form, The vibrational wavenumbers, harmonic force constants and infrared intensities were obtained from the MP2/6-31G* calculations, whereas the Raman activities and depolarization values were obtained from the RHF/6-31G* calculations. The spectra are interpreted in detail and the results are compared with those obtained for some related molecules. (C) 1998 John Whey & Sons, Ltd.