Kinetics of nucleophilic aromatic substitution in concentrated solutions of alkali metal methoxides in methanol

Abstract

The kinetics of nucleophilic aromatic substitution by methoxide ion on 11 substituted arenes have been studied at 20 °C using alkali metal (Li, Na, K) methoxides in methanol. Rate constants show a linear correlation with the excess basicity functions X for the three media, thus proving the applicability of the method to the interpretation of rate profiles in basic systems. The slopes m*_‡ are shown to depend on the solvation of the transition state leading to the Meisenheimer complex intermediates. The relationship between m*_‡ and standard state reactivities (log k₀) is discussed. The inversion in the relative reactivities of 2- and 4-chloronitrobenzene with increasing base concentration is explained.