Structural Aspects on Organosilicon Compounds

Abstract

Detailed knowledge about the bond lengths and bond distances in organosilicon compounds is available from nearly 200 crystal structure determinations. In the vast majority of such compounds the silicon atom is sp3 hybridized. The close similarity of silicon and carbon and the fact that a Si-C bond only is 20 % longer than a C-C bond makes it possible to replace carbon by silicon in organic molecules without drastic changes in their architecture. Biologically active molecules may thus be silicon-modified without loosing their activity. The recent finding of a cyclosiloxane (2,6-cis-diphenylhexamethylcyclotetrasiloxane) with a strong endocrinic activity but without any similarity with known biologically active molecules is most interesting and the crystal structure of this compound as well as some of related molecular species have now been determined. Accurate averages of bond lengths and bond angles in cyclic siloxanes have been calculated and different conformations of cyclotetra-siloxanes are discussed.