Infrared and Raman spectra, conformational stability, vibrational assignment, and ab initio calculations of chloromethyl isocyanate

Abstract The infrared (3200 to 400 cm −1 ) and Raman (3200 to 20 cm −1 ) spectra of gaseous and solid chloromethyl isocyanate, CICH 2 NCO, have been recorded. Also, the Raman spectrum of the liquid and qualitative depolarization values have been obtained. Additionally, infrared spectra have been recorded at various temperatures with the sample dissolved in liquid xenon. An assignment of the fundamental vibrations based on the infrared band contours, depolarization values and group frequencies is given and discussed. This assignment is supported by a normal coordinate analysis utilizing a force field obtained from ab initio calculations with the RHF/6-31G ∗ basis set as well as with electron correlation, MP2/6-31G ∗ . A complete equilibrium geometry has been determined by ab initio gradient calculations employing the RHF/3-21G ∗ , RHF/6-31G ∗ and MP2/6-31G ∗ basis sets. The potential surface governing internal rotation about the C-N bond is calculated to be consistent with a single minimum corresponding to a structure having the chlorine atom cis or near-cis to the NCO moiety. These results are compared with the corresponding quantities for ethyl isocyanate, CH 3 CH 2 NCO, and related compounds.