Rotational isomerism in poly(diorganosiloxane)-αω-diols

Abstract

The fundamental free hydroxy-stretching vibrations of a series of poly(diorganosiloxane)-αω-diols, diorganosilanediols, triorganosilanols, and alcohols have been examined at high resolution. The two or more overlapping absorptions given by many of the organosilanols have been satisfactorily explained in terms of rotational isomerism. The gauche-conformers of the trisiloxane-1,5-diols are, in many instances, stabilized by strong intramolecular hydrogen bonding of the hydroxy-groups, while in the poly(methylvinylsiloxane)-αω-diols and dibenzylsilanediol some isomers, as in certain alcohols, are stabilized by weak OH ⋯π interaction. Evidence is provided which disproves the concept of rotational freedom in siloxane bonds.