INFRARED AND RAMAN-SPECTRA, CONFORMATIONAL STABILITY, BARRIERS TO INTERNAL-ROTATION, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENTS FORDICHLOROFLUOROACETYL FLUORIDE

The Raman (2000 to 10 cm(-1)) spectra of dichlorofluoroacetyl fluoride , CCl2FCFO, of the vapor, liquid with qualitative depolarization ratio s and amorphous and crystalline states were recorded. The infrared (20 00 to 50 cm(-1)) spectra of the vapor and solid phases were also obtai ned and additional spectra as a solute in xenon were recorded at diffe rent temperatures. The data have been interpreted in terms of an equil ibrium between an anti (the two fluorine atoms being trans to each oth er) and a gauche conformer in the vapor and liquid phases, whereas onl y the anti conformer was present in the crystalline solid. From infrar ed band intensities of dichlorofluoroacetyl fluoride in xenon in the t emperature range 173 to 213 K a value of Delta H = 289 +/- 25 cm(-1) ( 828 +/- 72 cal/mol) was calculated with the anti conformer being the m ore stable form. Optimized geometries and conformational stabilities w ere derived from ab initio calculations using the basis sets RHF/3-21G , RHF/6-31G* and MP2/6-31G*, and all of the calculations predict the anti rotamer to be the most stable conformer. The vibrational frequenc ies were calculated using appropriate scaling factors, and the spectra are interpreted in detail. The results have been compared with those obtained for related molecules. (C) 1997 Elsevier Science B.V.