The conformers of bromomethyl dimethyl chlorosilane studied by vibrationalspectroscopy and ab initio methods

Bromomethyl dimethyl chlorosilane (CH2Br(CH3)(2)SiCl) was synthesised and t he infrared spectra of the vapour and of the amorphous and crystalline stat es at liquid nitrogen temperature were obtained. Additional spectra of the compound, isolated in argon, nitrogen and xenon matrices were recorded at 5 and 15 K. Raman spectra of the liquid were obtained at various temperature s between 295 and 173 K, and spectra of the amorphous and crystalline solid s were recorded. The compound is present as anti and gauche conformers in the vapour and in the liquid states. Various infrared and Raman bands present in these phases vanished upon crystallisation. Raman temperature studies in the liquid gav e a gauche-anti value of 1.0 +/- 0.3 kJ mol(-1), anti was the low energy co nformer and was also present in the crystal. The infrared bands diminishing in the argon, nitrogen and xenon matrix spectra after annealing to 28-60 K suggested that the anti conformer also had a slightly lower energy than ga uche in all the matrices. The conformational barrier was estimated to be 8- 10 kJ mol(-1). Ab initio calculations on different levels of approximation gave optimised geometries, infrared and Raman intensities and vibrational frequencies for the anti and gauche conformers. All calculations predicted anti as the low energy conformer. After scaling, a reasonably good agreement between the ex perimental and calculated wavenumbers for the two rotamers was obtained. (C ) 2000 Elsevier Science B.V. All rights reserved.