Kinetics of the reaction of phenyl picrates with phenoxide ions in water. Concerted or stepwise?

A kinetic study is reported of the exchange reactions of substituted phenoxide ions with some ring‐substituted 2,4,6‐trinitrophenyl ethers in water. The βrønsted diagrams formed by plotting log k , where k is the second‐order rate constant for reaction, versus p K a show a distinct change in slope when Δp K a  = 0 (Δp K a being the difference in p K a values of the leaving group and nucleophile). This is consistent with a two‐step process involving a discrete σ‐adduct intermediate rather than a concerted process. From the measured β values for forward and reverse processes, the overall effective charge map has been constructed. Copyright © 2013 John Wiley & Sons, Ltd.