RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENTS FOR CHLOROMETHYL METHYL SILANE

The infrared (3500 to 30 cm(-1)) spectra of gaseous and solid and the Raman (3500 to 10 cm(-1)) spectra of the liquid with quantitative depo larization ratios and solid chloromethyl methyl silane, ClCH2SiH2CH3, have been recorded. Similar data have also been recorded for the Si-d( 2) isotopomer. These data indicate that two conformers are present in the fluid states but only one conformer is present in the annealed cry stalline state. The mid-infrared spectra of the sample dissolved in li quified xenon as a function of temperature (-100 to -70 degrees C) hav e been recorded. Utilizing conformer pairs at 738 (gauche), 685 (gauch e), and 700 (trans) cm(-1) the enthalpy difference has been determined to be 180 +/- 18 cm(-1) (515 +/- 51 cal mol(-1)) with the gauche conf ormer the more stable species. However, in the spectrum of the solid, the trans conformer is the stable rotamer remaining after the sample i s well annealed. Utilizing the Si-H stretching frequencies from the in frared spectrum of the ClCH2SiHDCH3 isotopomer, the two Si-H bond dist ances are calculated to be 1.482 and 1.487 Angstrom for the gauche con former. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies are reported for both conformers f rom RHF/6-31G and/or MP2/6-31G* ab initio calculations. The gauche co nformer is predicted to be the more stable rotamer from both ab initio calculations in agreement with the experimental results. The other ca lculated quantities are compared to the experimentally determined valu es where applicable as well as with some corresponding results for som e similar molecules. (C) 1998 Elsevier Science B.V.