The Structure of Hexamethylcyclotrisiloxane as Determined by the Diffraction of Electrons on the Vapor

Abstract

Hexamethylcyclotrisiloxane vapor has been shown to have a structure incorporating a planar ring with larger oxygen valence angles (125±5°) than silicon valence angles (115±5°); the methyl groups extend above and below the plane of the ring, their equilibrium bond positions making a probable angle of 112±6° with silicon, the temperature motion of the methyl groups allowing an average change in the interatomic distances involved of about 0.09A, as compared with the normal temperature motion change of about 0.03A. The Si–O distances are 1.66±0.04A and the Si–C distances are 1.88±0.04A. The shortness of the Si–O distance suggests a larger ionic character of the bond than that indicated by the electronegativity table.