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 π-complex models. The oxygen atoms tend to form dative π 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.