Vibrational assignments and conformer stability determination of cyclobutyldichlorosilane by variable temperature Raman spectra in krypton solution

Abstract

The infrared spectrum (3100–300cm−1) in the gas phase and Raman spectrum (3100–150cm−1) of the liquid of cyclobutyldichlorosilane (c-C4H7SiHCl2) have been recorded. Variable temperature (−143°C to −123°C) studies of the Raman spectra (3100–300cm−1) dissolved in liquid krypton have been carried out. From these data, the experimental stabilities of the conformer have been determined to be Eq-g>Ax-t>Eq-t>Ax-g. The enthalpy difference between Eq-g and Ax-t has been determined from band pairs to be 85±10cm−1 (1.01±0.11kJmol−1) with the Eq-g conformer the more stable form. The enthalpy difference between Eq-g and Eq-t is 116±43cm−1 (1.39±0.52kJmol−1) and the enthalpy difference between Eq-g and Ax-g has been determined to be 138±42cm−1 (1.66±0.51kJmol−1) with the Eq-g conformer as the more stable form. The percentage of the equatorial gauche conformer is estimated to be 47% at ambient temperature. To support the spectroscopic study, ab initio calculations by the Møller–Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The infrared intensities, Raman activities, vibrational frequencies and band contours have been predicted from MP2(full)/6-31G(d) calculations and these theoretical values are compared to the experimental ones when available. The conformational stabilities have been predicted from theoretical calculations with basis sets up to 6-311+G(2d,2p) from both MP2(full) and density functional theory calculations by the B3LYP method. The results are discussed and compared to the corresponding properties of some related molecules.