The kinetics of nucleophilic aromatic substitution by methoxide ion on 11 substituted arenes have been studied at 20-degrees-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*double-ended dagger are shown to depend on the solvation of the transition state leading to the Meisenheimer complex intermediates. The relationship between m*double-ended dagger and standard state reactivities (log k(0)) is discussed. The inversion in the relative reactivities of 2- and 4-chloronitrobenzene with increasing base concentration is explained.
Kinetics of Nucleophilic Aromatic Substitution in Concentrated Solutions of Alkali Metal Methoxides in Methanol
BAGNO, ALESSANDRO;SCORRANO, GIANFRANCO;
1991
Abstract
The kinetics of nucleophilic aromatic substitution by methoxide ion on 11 substituted arenes have been studied at 20-degrees-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*double-ended dagger are shown to depend on the solvation of the transition state leading to the Meisenheimer complex intermediates. The relationship between m*double-ended dagger and standard state reactivities (log k(0)) is discussed. The inversion in the relative reactivities of 2- and 4-chloronitrobenzene with increasing base concentration is explained.Pubblicazioni consigliate
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