The SN mechanism in aromatic compounds. Part XL. Activating effects of groups attached to the ring by a sulphur atom

Abstract

Kinetic data are presented for the alkaline methanolysis of a series of 4-substituted fluorobenzenes, in which the substituents are joined to the ring through sulphur, viz. SMe, SPh, SCF₃, SOMe, SO₂Me, SO₂Ph, and SO₂CF₃. The Hammett substituent constants (σ^–) estimated at 100° are: 0.27; 0.36; 0.66; 0.77; 1.00; 1.04: 1.40. These are compared with values for COMe, NO, and NO₂groups. It is suggested that in the sequence of saturated groups SCH₃to SCF₃, a small conjugative effect becomes evident. The possibility of a favourable polarizability effect is also considered. The ability of SR groups to activate both S_E and S_NAr reactions is discussed and brief comparison made with OR groups.