Infrared and Raman spectra and conformational equilibrium of chloromethyl dimethyl chlorosilane

The infrared spectra of chloromethyl dimethyl chlorosilane (CH2Cl-(CH3)(2) SiCl) were recorded In the vapour phase and as amorphous and crystalline solids in the 4000-50 cm(-1) range and isolated in argon, nitrogen and xenon matrices at ca. 5 K. Raman spectra were recorded at room temperature and at various temperatures between 295 and 188 K. Spectra of the amorphous and crystalline solids were obtained at 80 and at 180 K. The compound exists in two conformations, anti and gauche, and six infrared and eight Raman bands present in the vapour, liquid and amorphous slates vanished after crystallization. The spectra were interpreted in terms of the anti conformer being the low energy form in the vapour and liquid phases and also being present in the crystal. The intensity variations with temperature of four band pairs in the Raman spectra of the liquid were employed in van't Hoff plots and gave a value of 0.7 +/- 0.2 kJ mol(-1) for Delta(con)H. Very small changes were detected when the matrix spectra were annealed to 35 K (argon) or 32 K (nitrogen). Significant spectral changes were observed when xenon matrices were annealed to 40 K, revealing that the anti conformer was also more stable in this matrix. Ab initio calculations were carried out with the Gaussian 94 program at various levels of approximation including second order Moller-Plesset perturbation; optimized geometries, infrared and Raman intensities and the vibrational frequencies for the anti and gauche conformers were calculated. After appropriate scaling a reasonably good agreement was obtained between the experimental and calculated wavenumbers for both conformers.