Vibrational spectra and rotational isomerism of methyl methylsilyl sulphide

Infrared and Raman spectra of methyl methylsilyl sulphide are measured for the liquid and solid states. The fundamental vibrations are assigned and the normal vibrations calculated for two possible rotational isomers about the Si-S bond. Two different solid spectra are obtained, one corresponding to the trans form and the other to the gauche form; the liquid spectrum shows the presence of both forms. The gauche form is more stable than the trans form in the liquid state by 80 ± 50 cal mol^?1. The crystallization process indicates that the freezing and melting points of the trans form are slightly higher than those of the gauche form.