Conformational stability, barriers to internal rotation, vibrational assignment and ab initio calculations of oxalyl chloride

The Raman spectra (2000-10 cm(-1)) of gaseous, liquid and solid oxalyl chloride, (CClO)(2), have been recorded, and the Raman spectrum of the liquid with qualitative depolarization values has been obtained. In addition to the six symmetry permitted Raman lines for the trans conformer, there are eight more Raman lines observed in the spectrum of the gas (ten for the liquid) which must be assigned to a second conformer. These data have been interpreted on the basis of a more stable trans rotamer and high-energy gauche conformer in equilibrium for the fluid phases. Variable-temperature studies of the Raman spectrum have been carried out and a conformational enthalpy difference of 289 +/- 110 cm(-1) (827 +/- 315 cal mol(-1)) has been obtained for the gas. Additionally, variable-temperature studies of the infrared spectrum of the sample dissolved in xenon gave an enthalpy difference of 111 +/- 49 cm(-1) (317 +/- 140 cal mol(-1)). The CClO wag for the trans conformer has been assigned at 700 cm(-1) which is a much higher frequency than any previously reported value for this fundamental. Assignments are also provided for most of the fundamentals for the gauche conformer. All these data are compared with the corresponding quantities obtained from ab initio calculations employing the RHF/3-21G*, RHF/6-31G*, RHF/6-311(+)G*, and MP2/6-31G* basis sets. These data are also compared to the corresponding quantities for some similar molecules.