Kinetic and Theoretical Studies on Pyridinolysis of 2,4-Dinitrophenyl X-Substituted Benzoates: Effect of Substituent X on Reactivity and Mechanism

摘要: Second-order rate constants (k N ) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-NO 2 with a series Z-substituted pyridines in 80 mol % O/20 DMSO at 25.0 ± 0.1 °C. The Bronsted-type plots exhibit downward curvature (e.g., β 0.89 ∼ 0.96 when pK 9.5), indicating that the reaction proceeds through stepwise mechanism change rate-determining step (RDS). 0 , defined as center Bronsted curvature, has analyzed to be 9.5 regardless electronic nature substituent X benzoyl moiety. Dissection k into microscopic 1 /k -1 ratio revealed is governed by but not. Theoretical calculations also support argument moiety does not influence ratio.