X-ray diffraction investigation of siloxanes. II. Dependence of the structure of cyclic trisiloxanes on the nature of organic substituents at the silicon atom

The structure of six cyclic trisiloxane compounds with various combinations of carbon and oxygen-containing organic radicals Me, Ph, 2mPh, and 3mPh attached to the silicon atoms and lying in different positions of the trisiloxane cycle has been studied. The Si-O bond lengths vary within wide limits (1.607(5)–1.643(2) Å). Introduction of one or two 2mPh or 3mPh oxygen-containing radicals in the 1,1-position of the trisiloxane ring results in Si-O interatomic distances shortened to 1.624(3) Å. When two 3mPh radicals are in the 1,3-positions, the Si-O bond length decreases to 1.607(5) Å. The calculated charges on the silicon and oxygen atoms of the siloxane ring indicated that there is poor correlation between the charged state of the silicon atom and the Si-O bond length.