Raman and infrared spectra, conformational stability, normal coordinate analysis, ab initio calculations and vibrational assignment of 1-chloro-1-methylsilacyclobutane

The Raman spectrum (3500-30 cm(-1)) of liquid 1-chloro-1-methylsilacyclobut ane, c-C3H6SiCl(CH3), was recorded and quantitative depolarization values w ere obtained. Additionally, the infrared (3500-40 cm(-1)) spectra of the ga s and solid were recorded. Both the axial and equatorial (with respect to t he methyl group) conformers were identified in the fluid phases. Variable t emperature (-55 to -100 degrees C) studies of the infrared spectra of the s ample dissolved in liquid xenon were carried out. From these data, the enth alpy difference was determined as 178 +/- 15 cm(-1) (2.13 +/- 0.18 kJ mol(- 1)), with the axial conformer being the more stable form and the only confo rmer remaining in the polycrystalline solid, A complete vibrational assignm ent is proposed for the axial conformer and many of the fundamentals of the equatorial conformer were also identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force cons tants. Complete equilibrium geometries, conformational stabilities, harmoni c force fields, infrared intensities, Raman activities and depolarization r atios were determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311++G** basis sets at the levels of restricted Hartree-P ock (RHF) and/or Moller-Plesset (MP) to second order. The results are discu ssed and compared with those obtained for some similar molecules. Copyright (C) 1999 John Wiley & Sons, Ltd.