Molecular vibrations and rotational isomerism of chloro(isopropyl)silanes (CH3)2CHSiCl3-n(CH3)n (n = 0–3)

Abstract

Abstract The i.r. and Raman spectra of the (CH 3 ) 2 CHSiCl 3- n (CH 3 ) n ( n = 0–3) series of molecules were measured for the liquid and solid states. Rotational isomerism was investigated on the basis of the spectral observations and the normal coordinate treatment. For dichloro(isopropyl)methylsilane and chloro(isopropyl)dimethylsilane, two rotational isomers coexisted in the liquid state and only one of them persisted in the solid state. It was shown from the enthalpy differences between the isomers that the conformation with more methyl—chlorine gauche -dispositions and fewer methyl—methyl gauche -dispositions was more stable than the other. The barriers to internal rotation about a skeletal CSi axis were roughly estimated from the enthalpy differences and the torsional frequencies of the skeleton.