The Molecular Vibrations and the Rotational Isomerism of (Chloromethyl)methylsilane

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Abstract
The infrared spectra of (chloromethyl)methylsilane and its deuterated species have been measured in the gaseous, liquid, and crystalline states. The normal vibration calculation has been carried out using a modified Urey-Bradley force field. It has been concluded that, in the gaseous and liquid states, there exist both the trans and gauche isomers, while only the former persists in the crystalline state. For ClCH2SiD2CH3, a different spectral pattern has sometimes been recorded in the crystalline state before the sample has been annealed enough. It has been concluded that the persisting isomer is in the gauche form in this metastable crystalline state. The trans and gauche isomers have been found, from the temperature dependence of the relative intensities of the spectra, to have nearly the same energy in the liquid state. From the solvent effects of the spectra, the trans isomer has been found to be more polar than the gauche isomer. Therefore, if the C–Cl bond moment is assumed to have the direction of C+–Cl−, the group moment of the C2SiH2 part of the molecule must be in the direction of (Remark: Graphics omitted.) on the bisector of the C–Si–C angle. The vibrational assignments have been worked out taking into account the results of the normal vibration calculations and the reported assignments for chloromethylsilane, dimethylsilane, and ethylmethylsilane.