ABSTRACT
The stereoelectronic effect of a sulfur group depends upon whether the central sulfur atom is di-, tri-, tetra-, or hexacoordinate. Divalent sulfenyl sulfur can be either electron-releasing or electron-accepting by induction or electron sharing through conjugation. This chapter examines the effects of the sulfur groups, begins with dicoordinate sulfur and progressing by increasing cordination number. The original L. P. Hammett a value from the acid dissociation of substituted benzoic acids is +0. 07 for p-CH3S–, which indicates that the dicoordinate sulfur group is electron-withdrawing. In assessing the electron-withdrawing nature of dicoordinate sulfur groups, the 3d-orbital resonance effect also has to be taken into consideration. Both tricoordinate and tetracoordinate sulfur groups are electron-withdrawing; most of the studies have been made on the carbanion-stabilizing behavior of these groups. Quantitative data showing the electron-accepting effects of the tricoordinated and tetracoordinated sulfur groups can be found in measurements of the relative reactivities for nucleophilic substitution of chlorobenzene derivatives.
