Raman and infrared spectra, conformational stability, barriers to internal rotation, ab initio calculations and vibrational assignment of dichloroacetyl fluoride

The Raman spectra (3200‐10 cm−1) of dichloroacetyl fluoride (CHCL2CFO) of the gas, liquid (with qualitative depolarization ratios) and solid were recorded. The infrared spectra (3200‐30 cm−1) of the gas and solid were also obtained. All of these data indicate a trans/gauche equilibrium in the gas and liquid whereas only the gauche conformation remains in the solid. A complete vibrational assignment is proposed for both conformers based on the Raman depolarization data, infrared band contours, group frequencies and normal coordinate calculations. From the studies of the Raman spectra at various temperatures, the enthalpy difference between the stable conformers was determined to be 315 ± 68 cm−1 (0.90 ± 0.19 kcal mol−1) (1 kcal = 4.184 kJ) and 180 ± 4 cm−1 (0.51 ± 0.01 kcal mol−1) for the gas and liquid, respectively, with the trans conformer being more stable in the gas but the gauche conformer more stable in the liquid. These experimental results are compared to those obtained from ab initio Hartree‐Fock gradient calculations with the RHF/3‐21G* and RHF/6‐31G* basis sets, and to the corresponding quantities obtained for some similar molecules.