ABSTRACT
Substitution ranks with oxidation and reduction as one of the some major reactions which take place on the sulfur (S) atom. This chapter looks at actual data of the interesting mechanistic aspects of nucleophilic substitution and begins with the dicoordinate sulfur compounds. In the nucleophilic substitution on the sp3 carbon, the SN1 mechanistic path involves the initial formation of the carbocation, and occurs especially when the carbocation is stabilized, as in the case of t-alkyl carbocations. The larger steric effects in the nucleophilic substitution on the Bunte salt are due to the formation of a σ-sulfurane intermediate. Stereochemistry is the most interesting part of nucleophilic substitution, or ligand exchange on the S atom. Thiophilicity is the ability of a nucleophile to attack an S atom. It is important since the rate-determining step in most nucleophilic substitutions is the attack of nucleophile on the sulfenyl sulfur atom even in the ligand exchange process involving the incipient σ-sulfurane intermediate.
