An ab initio quantum chemical study of cumulative double bonds: stability of various conformers and charge distribution analysis. Part I. XY 2H 2 hierarchy (X=O, S, Se and Y=N, P, As)

Abstract

In this paper, various properties of XY 2H 2 (H–Y X Y–H) (X=O, S, Se and Y=N, P, As) hierarchy have been studied using ab initio quantum chemical methods. General geometrical tendencies have been observed for all members of this family as well as some distinguished geometrical characters of OP 2H 2 and OAs 2H 2 molecules. The energetic calculations reveal that in four molecules (SN 2H 2, SeN 2H 2, OP 2H 2 and OAs 2H 2), ZZ is the most stable conformer and EZ and EE stand on subsequent stability ranks. So it has been demonstrated that ZZ's unusual stability is not confined to sulfur diimides. The charge distribution analysis focusing on atomic partial charge distribution reveals that indeed a common property, namely significant charge separation takes place in the above-mentioned molecules. To characterize and stress on this ZZ's unusual and possibly unprecedented stability relative to EZ and EE, we have proposed the name ‘Z-effect’.