Spectra and structure of silicon-containing compounds. XXX. Raman and infrared spectra, conformational stability, vibrational assignment of chloromethyl silyl dichloride

Abstract

The Raman spectra (3200–30 cm −1) of liquid and solid, and infrared spectra of gaseous and solid chloromethyl silyl dichloride, ClCH 2SiHCl 2, have been recorded. Variable temperature (−105 to −150 °C) studies of the infrared spectra of the sample dissolved in liquid krypton have been carried out. From these data, the enthalpy difference was determined to be 363±40 cm −1 (4.34±0.48 kJ mol −1), with the more stable form being the gauche conformer, which is consistent with the prediction from ab initio calculations at both the Hartree-Fock level and with full electron correlation by the perturbation method to second order. It is estimated that 92% of the sample is in the gauche form at ambient temperature. A complete vibrational assignment is proposed for the gauche conformer and several of fundamentals of the trans conformer based on infrared band contours, relative intensities, depolarization values, and group frequencies, which is supported by normal coordinate calculations utilizing the force constants from the ab initio MP2/6-31G(d) calculations. The r 0 SiH bond distances of 1.476 and 1.472 Å have been obtained for the trans and gauche conformers, respectively, from the silicon–hydrogen stretching frequencies. The optimized geometries have also been obtained from ab initio calculations utilizing several different basis sets with full electron correlation by the perturbation method up to MP2/6-311+G(2d,2p). The results are discussed and compared to some corresponding results for several related molecules.