FT-Raman spectrum and conformational stability of liquid chlorocarbonyl isocyanate

Abstract The FT-Raman spectrum of liquid chlorocarbonyl isocyanate, ClC(O)NCO, has been recorded from 2500 to 75 cm −1 . The observed bands have been assigned in terms of the more stable trans conformer (isocyanate group trans to the carbonyl bond) and less stable cis conformer. Several conformer pairs have been observed which have been used to obtain the enthalpy difference between the conformers from the relative intensities of the conformer peaks. The determined ΔH value is 262 ± 119 cm −1 (749 ± 340 cal/mol) which is in good agreement with the previously reported value of 230 ± 28 cm −1 (658 ± 80 cal/mol) which was obtained from a temperature study of the Raman spectrum. The fundamental Raman frequencies and Raman intensities which have been determined experimentally are compared to those obtained from ab initio Hartree-Fock gradient calculations utilizing the 6-31G* basis set. These results are compared to some previous results on this molecule.