Conformational stability of ethyl chlorogermane from temperature-dependent FT-IR spectra of krypton solutions and r0 structural parameters of methyl chlorogermane and ethyl germane

Abstract

The Raman spectra (3200–30 cm −1) of liquid and solid, and infrared spectra of gaseous and solid ethyl chlorogermane, CH 3CH 2GeH 2Cl, 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 has been determined to be 143±30 cm −1 (1.71±0.36 kJ mol −1), with the more stable form, the gauche conformer, which is consistent with the prediction from ab initio calculations at both the Hartree–Fock level and with electron correlation by the perturbation method to second order. It is estimated that 80% of the sample is in the gauche form at ambient temperature. A complete vibrational assignment is proposed for both the gauche and trans conformers 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 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 r 0 adjusted structural parameters for methyl chlorogermane and ethyl germane have been obtained from a combination of the previously reported microwave rotational constants and ab initio predicted parameters. The results are discussed and compared to some corresponding results for several related molecules.