Kinetics of reversible thiolate ion addition to substituted .beta.-nitrostyrenes in water. Radicaloid transition state or principle of nonperfect synchronization?

Abstract

The kinetics of reversible nucleophilic thiolate ion (RS - with R=n-Bu, HOCH 2 CH 2 , MeO 2 CCH 2 CH 2 and MeO 2 CCH 2 ) addition to Z-substituded β-nitrostyrenes (Z=4-Me 2 N, 4-MeO, 4-MeS, H, 3-Cl, 4-Cl, 3-CN, 4-CN, and 3-NO 2 ), to form ArCH(RS)CH=NO 2 - , have been measured in water at 20 o C. Rate constants in the forward (k 1 ) and reverse direction (k -1 ) and equilibrium constants (K 1 ) correlate reasonably well with Hammet σ-constants for the non-π-donor substituents but show deviations for the π-donors 4-Me 2 N, 4-MeO, and 4-MeS