Raman and infrared spectra, conformational stability, and ab initio calculations for chloromethyl methyl sulfide

The Raman (3500–20 cm−1) and infrared (3500–40 cm−1) spectra of gaseous and solid chloromethyl methyl sulfide [chloro(methylthio)methane], CICH2SCH3, and the corresponding deuterated molecule, CICD2SCD3, were recorded. Additionally, the Raman spectra of the liquids were recorded from 3500 to 50 cm−1 and qualitative depolarization values were obtained. These data were interpreted on the basis that only the gauche conformer (methyl group gauche to the chlorine atom) is present in all three physical states. A complete vibrational assignment is given for the normal and d5-isotopomer. Ab initio calculations were carried out with the RHF/6–31G* basis set, and also with full electron correlation by the perturbation method to second order (MP2) with the 6–31G* and 6–311+G** basis sets, to obtain the structural parameters, relative conformational stabilities, harmonic force constants, Raman and infrared intensities and fundamental wavenumbers. The fundamental vibrational wavenumbers and barriers to internal rotation which were obtained experimentally are compared with those obtained from the MP2/6–31G* calculation. From the ab initio calculations the gauche conformer is estimated to be more than 10.22 kJ mol−1 more stable than the trans conformer. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules. Copyright © 2000 John Wiley & Sons, Ltd.