CONFORMATIONAL STABILITY. BARRIERS TO INTERNAL ROTATION. VIBRATIONAL ASSIGNMENT AND AB INITIO CALCULATIONS OF OXALYL CHLORIDE AND OXALYL CHLOROFLUORIDE

Abstract

The Raman spectra (2000 to $10 cm^{-1}$) of gaseous, liquid and solid oxalyl chloride and oxalyl chlorofluoride have been recorded and the Raman spectra of the liquids have been obtained with qualitative depolarization ratios. These data have been interpreted on the basis of a more stable trans and high energy gauche conformational equilibrium for the fluid phases of the chloride but a trans/cis equilibrium for the chlorofluoride. Additionally, variable temperature studies of the Raman spectra of the chloride have been carried out and conformational enthalpy differences of 300 and $150 cm^{-1}$ have been obtained for the gas and liquid, respectively. Estimates were also made for the enthalpy differences between conformers from the relative intensities of several conformer pairs utilizing the relative Raman activities obtained from the ab initio calculations. Revised vibrational assignments are provided for both molecules from these new data. All these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the $RHF/3-21G^{\ast}, RHF/6-31G^{\ast} RHF/6-311+G^{\ast}$, and/or $MP2/6-31G^{\ast}$ basis sets. These data are also compared to the corresponding quantities for some similar molecules.