Vibrational spectra and structure(s) of X(OR)₄ molecules with X C,: Si and R = methyl, ethyl

Vibrational spectra of tetramethoxymethane (TMM), tetraethoxymethane (TEM), tetramethoxysilane (TMS) and tetraethoxysilane (TES) have been recorded and assigned. DTA curves and temperature vs. time curves have been recorded in the region −150 to + 30°. No transition points have been observed, melting ranges are −1 to +2 (TMM); −16 to −12 (TEM); +10 to +16 (TMS) and −71 to −68° (TES). The liquid state of tetramethoxymethane (TMM) contains two rotamers; the skeleton C(OC) 4 may have S 4 or D 2d symmetry. The S 4 form is about 1 kcal/mole more stable than the D 2d form of TMM in the liquid. Solid TMM consists probably of the D 2d configuration only. There is no distinction between either configuration in tetramethoxysilane (TMS) as the rotation of methoxy groups around their SiO axes is apparently free for practical purposes. The methyl group of an ethoxy group in X(OC 2 H 5 ) 4 may occupy a gauche or a trans position relative to its XO bond. Rotational isomerism of this kind is probably present in tetraethoxymethane (TEM). Rotational isomerism is probably absent in tetraethoxysilane (TES).