SPECTRA AND STRUCTURE OF SILICON-CONTAINING COMPOUNDS .23. RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, VIBRATIONAL ASSIGNMENT ANDAB-INITIO CALCULATIONS OF DIMETHYL VINYL CHLOROSILANE

The infrared (3500 to 40 cm(-1)) and Raman (3500 to 20 cm(-1)) spectra of gaseous and solid dimethyl vinyl chlorosilane, CH2CHSi(CH3)(2)Cl, have been recorded. Additionally, the Raman spectrum of the Liquid has been recorded and qualitative depolarization values obtained. Both th e cis and gauche conformers have been identified in the fluid phases b ut only the gauche conformer remains in the solid. Variable temperatur e (-60 to -100 degrees C) studies of the infrared spectra of dimethyl vinyl chlorosilane dissolved in liquid xenon have been recorded. From these data the enthalpy difference has been determined to be 41 +/- 9 cm(-1) (117 +/- 26 cal mol(-1)) with the gauche conformer the more sta ble rotamer. A complete vibrational assignment is proposed for the gau che conformer based on infrared and Raman relative intensities, depola rization values and group frequencies. Several of the fundamentals for the cis conformer have also been identified. The vibrational assignme nts are supported by normal coordinate calculations. Complete equilibr ium geometries have been determined for both rotamers by ab initio cal culations employing the 3-21G and 6-31G* basis sets at the levels of the restricted Hartree-Fock (RHF) and Moller-Plesset (MP) to second or der. The frequencies for the normal modes and the potential energy ter ms for the conformer interconversion have been calculated at the MP2/6 -31G level. The results are discussed and compared to those obtained for some similar molecules.