THE VIBRATIONAL-SPECTRA, INCLUDING MATRIX-ISOLATION, CONFORMATIONS AND AB-INITIO CALCULATIONS OF BROMOMETHYL DIMETHYL CHLOROSILANE

A vibrational spectroscopic study of bromomethyl dimethyl chlorosilane (CH2Br-(CH3)(2)SiCl) was carried out. Infrared spectra of the vapour, the amorphous and crystalline solids at liquid nitrogen temperature, and spectra of argon and nitrogen matrices (1:1000) at about 5 K were recorded. Raman spectra of the liquid were obtained at five temperatur es between 295 and 190 K, and spectra of the crystalline solid were re corded. Owing to restricted rotation around the C-Si bond, the compoun d apparently exists as anti and gauche conformers. Approximately five IR and Raman bands present in the fluid phases vanished upon crystalli zation. From intensity variations with temperature in the Raman spectr a of the liquid, a Delta H-o value of 1.0 +/- 0.4 kJ mol(-1) was obtai ned. The high energy conformer bands did not vanish in the matrix spec tra after annealing to approximately 39 K in the argon matrix, suggest ing a barrier higher than 10 kJ mol(-1). Ab initio calculations were c arried out with the GAUSSIAN 94 program using the basis sets HF/3-21G and HF/6-311G; optimized geometries, IR and Raman intensities, and t he vibrational frequencies for the anti and gauche conformers were cal culated. After appropriate scaling, reasonably good agreement was obta ined between the experimental and calculated wavenumbers for the anti and gauche conformers, suggesting the anti conformer re, be the more s table and present in the crystal. (C) 1997 Elsevier Science B.V.