Spectra and structure of silicon‐containing compounds. XXXIII — Raman and infrared spectra, conformational stability and vibrational assignment of chloromethylsilyl bromide

Abstract

AbstractThe Raman spectra (3200 to 30 cm−1) of liquid and solid and the infrared spectra of gaseous and solid chloromethylsilyl bromide, ClCH2SiH2Br, were recorded. Utilizing three conformer pairs from the Raman spectrum of the liquid along with their ab initio predicted activities, the enthalpy difference of 216 ± 22 cm−1 (2.58 ± 0.26 kJ mol−1) was obtained with the trans conformer the more stable form. Variable temperature (−105 to 150° C) studies of the infrared spectra of the sample dissolved in liquid krypton were carried out and from these data, the enthalpy difference was estimated to be 250 ± 50 cm−1 (2.99 ± 0.60 kJ mol−1), again with the more stable form being the trans conformer. These values are consistent with the prediction from ab initio calculations both at the Hartree–Fock level and with full electron correlation by the perturbation method to second order. It is estimated that 37 ± 6% of the sample is in the gauche form at ambient temperature. Only the trans conformer remains in the spectra of the solid. A complete vibrational assignment is proposed for the trans conformer and also several of fundamentals of the gauche 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 optimized geometries and conformational stabilities were also been obtained from ab initio calculations utilizing two additional basis sets with full electron correlation by the perturbation method. Estimates were made of the r0 structural parameters based on the predicted structural parameters from ab initio MP2/6–311 + G(d,p) calculations. The results are discussed and compared with some corresponding results for some related molecules. Copyright © 2002 John Wiley & Sons, Ltd.