Some semi-empirical molecular orbital studies of the origin of conformational preferences for free S₂O₄^2- and N₂O₄

Abstract

The results of some semi-empirical MO-CI calculations of the barriers to rotation around the S-S and N-N bonds of S₂O₄^2- and N₂O₄ are reported. The calculated barriers are expressed in terms of atomic, cis O-O overlap, coulombic repulsion and exchange contributions. The barrier analysis for N₂O₄ shows that cis O-O overlap stabilizes the planar relative to the skew conformer, whereas for free S₂O₄^2-, reduced coulombic repulsions stabilize the trans conformer relative to the eclipsed. Some CNDO/2 estimates of the rotation barrier for S₂O₄^2- are also reported.