Conformational stability, vibrational spectra and ab initio calculations for chloromethyl methyl silane and chloromethyl methyl difluorosilane

The infrared spectra of gaseous and solid chloromethyl methyl silane, ClCH2SiH2CH3, and chloromethyl methyl difluorosilane, ClCH2SiF2CH3, were recorded. Additionally, the variable temperature infrared spectra of the sample dissolved in liquid krypton and/or xenon were obtained. Both the trans and gauche conformers are present in the fluid phases but only the trans conformer is present in the solid for both molecules. The enthalpy difference between the two conformers for chloromethyl methyl silane was determined to be 180 +/- 15 cm(-1) (2.16 +/- 2.16 +/- 0.18 kJ/mol) and for chloromethyl methyl difluorosilane 236 +/- 15 cm(-1) (2.82 +/- 0.17 kJ/mol) in xenon with the gauche conformers more stable for both molecules. The enthalpy value for the silane in krypton is 181 +/- 18 cm(-1) (2.16 +/- 0.09 kJ/mol). Ab initio calculations were carried out at the RHF/6-31G* and MP2/6-31G* levels for both molecules from which structural parameters and conformational stabilities were determined. (C) 1999 Elsevier Science B.V. All rights reserved.