Stable conformations of aliphatic disulfides: influence of 1,4 interactions involving sulfur atoms.

The present state of knowledge of the stable conformations of the XCCSSCCX fragment (in which X is any saturated group) of aliphatic disulfides is examined. In particular, the evidence for the existence of attractive 1,4 interactions between CH groups and S atoms across C-S bonds and their influence on the potential function for rotation about C-S bonds is discussed. The effects of similar attractive interactions between NH groups and S atoms on the potential function for rotation about C-C bonds also are considered. It is concluded that weak attractive interactions between CH groups and S atoms are capable of stabilizing rotamers with unusually low (about 30 degrees) values of the SS-CC dihedral angle.