Abstract
Second-order rate constants have been measured spectrophotometrically for reactions of 2,6-dimethoxy-3,5-dinitropyridine 1 with 4-X-substituted phenoxide anions (X = OMe, Me, H, Cl, and CN) 2a-e in aqueous solution at various temperatures. The effect of phenoxide substituents on the reaction rate was examined quantitatively on the basis of kinetic measurements, leading to nonlinear correlations of H and S with Hammett's substituent constants (sigma). Each Hammett plots exhibits two intersecting straight lines for the reactions of 1 with the phenoxide anions 2a-e, whereas the Yukawa-Tsuno plots for the same reactions are linear. The large negative values (-4.03 to -3.80) obtained for the reactions of 1 with the phenoxide anions possessing an electron-donating group supports the proposal that the reactions proceed through a single-electron transfer mechanism. (C) 2016 Wiley Periodicals, Inc.