VIBRATIONAL-SPECTRA, NORMAL VIBRATIONS AND ROTATIONAL-ISOMERISM OF ALKYLSILANES .1. PROPYLSILANE, BUTYLSILANE AND THEIR SI-PERDEUTERIUM COMPOUNDS

The infrared and Raman spectra of propylsilane, butylsilane and their Si-perdeuterium compounds were measured for the liquid and crystalline solid states. The gaseous-state spectra of propylsilanes were also recorded. The spectra were analysed on the basis of the normal coordinate treatment with a consistent set of force constants for unbranched alkylsilanes. The CSi stretching wavenumbers are well correlated with the conformation of the (C)CH2CH2(SiH3) group. In the crystalline solid state, propylsilane takes the trans form and butylsilane takes the trans-trans form. All the staggered conformers except the gauche-gauche' form of butylsilane were shown to exist in the liquid state. The enthalpy difference between the trans and gauche forms of propylsilane was found to be 600-650 cal mol-1 in the liquid state, the trans form being more stable. © 1979.