Cyclic delocalization of the oxygen lone pair electrons in the unusual structures of disilaoxirane and 1,3-cyclodisiloxane

Significant interactions between the n orbitals of the oxygen lone pair electrons and the d-type polarization functions of the silicon atoms in disiloxane (1) disilaoxirane (2), and 1,3-cyclodisiloxane (3) were demonstrated by numerical evaluation of the bond interactions. The calculated Lewis index showed that the Si-O double bond model contributes more than the single bond and pi-complex models. The oxygen atoms tend to form dative pi bonds to the silicon atoms or be tetravalent. In the ring systems 2 and 3, the lone pair electrons delocalize in a cyclic manner by the interaction of the p orbital of the oxygen lone pair and the d functions of the Si atoms. The cyclic delocalization is responsible for the short Si-Si bond in 2 and the short nonbonded Si ... Si distance of 3. The elongation of the distance between the silicon atoms in the protonated and cation radical species of 2 and 3 was predicted from the cyclic delocalization and confirmed by ab initio molecular orbital calculations.