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 temperatures between 295 and 190 K, and spectra of the crystalline solid were recorded. Owing to restricted rotation around the C-Si bond, the compound apparently exists as anti and gauche conformers. Approximately five IR and Raman bands present in the fluid phases vanished upon crystallization. From intensity variations with temperature in the Raman spectra of the liquid, a Delta H-o value of 1.0 +/- 0.4 kJ mol(-1) was obtained. The high energy conformer bands did not vanish in the matrix spectra after annealing to approximately 39 K in the argon matrix, suggesting a barrier higher than 10 kJ mol(-1). Ab initio calculations were carried out with the GAUSSIAN 94 program using the basis sets HF/3-21G* and HF/6-311G*; optimized geometries, IR and Raman intensities, and the vibrational frequencies for the anti and gauche conformers were calculated. After appropriate scaling, reasonably good agreement was obtained between the experimental and calculated wavenumbers for the anti and gauche conformers, suggesting the anti conformer re, be the more stable and present in the crystal. (C) 1997 Elsevier Science B.V.