THE VIBRATIONAL-SPECTRA AND CONFORMERS OF CHLOROMETHYL DIMETHYL CHLOROSILANE

The IR spectra of chloromethyl dimethyl chlorosilane (CH2Cl-(CH3)(2)Si Cl) were recorded as a vapour and as amorphous and crystalline solids in the 4000-50 cm(-1) range and isolated in argon and nitrogen matrice s at ca, 5 K, Raman spectra were recorded at room temperature and at v arious temperatures, partly as a super cooled liquid between 295 and 1 88 K and spectra of the amorphous and crystalline solids were obtained at 80 K and at 185 K. The compound exists in anti and gauche conforme rs, and six IR bands and Raman bands present in the vapour, liquid and amorphous states vanished upon crystallization. The intensity variati ons with temperature of four band pairs in the Raman spectra of the li quid were employed in van't Hoff plots and gave a value of 0.7 +/- 0.2 kJ mol(-1) for Delta H degrees (gauche-anti). The anti conformer had the lower energy and was also present in the crystal, Only small chang es were detected when the matrix spectra were annealed to 39 K (argon) or 34 K (nitrogen) suggesting a conformational barrier larger than 10 kJ mol(-1). Ab initio calculations were carried out with the GAUSSIAN 94 program using the basis sets HF/3-21G, HF/6-31G*:, HF/6-311G* and MP2/6-311G; optimized geometries, IR and Raman intensities and the v ibrational frequencies for the anti and gauche conformers were calcula ted. After appropriate scaling a reasonably good agreement was obtaine d between the experimental and calculated wavenumbers for both conform ers. (C) 1997 Elsevier Science B.V.