SPECTRA AND STRUCTURE OF SILICON-CONTAINING COMPOUNDS .22. RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, VIBRATIONAL ASSIGNMENT ANDAB-INITIO CALCULATIONS OF METHYLVINYLDICHLOROSILANE

The infrared (3500-40 cm(-1)) and Raman (3500-20 cm(-1)) spectra of ga seous and solid methylvinyldichlorosilane, CH2CHSiCl2CH3, have been re corded. Additionally, the Raman spectrum of the liquid has been record ed and qualitative depolarization values obtained. Both the cis and ga uche conformers have been identified in the fluid phases but only the cis conformer remains in the solid. Variable temperature (-60 to -100 degrees C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy diff erence has been determined to be 77 +/- 8 cm(-1) (220 +/- 23 cal mol(- 1)), with the cis conformer being the more stable rotamer. A complete vibrational assignment is proposed for the cis conformer based on infr ared band contours, relative intensities, depolarization values and gr oup frequencies. Several of the fundamentals for the gauche conformer have also been identified. The vibrational assignments are supported b y normal coordinate calculations. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 3-21G and 6-31G* basis sets at the levels of restricted Hartree- Fock (RHF) and Moller-Plesset (MP) to second order. The frequencies fo r the normal modes and the potential energy terms for the conformer in terconversion have been obtained from the RHF/6-31G calculation. The results are discussed and compared to those obtained for some similar molecules.