Nucleophilic substitution of benzyl benzenesulphonates with anilines in methanol-acetonitrile mixtures. Part 2. Variation in transition-state structure

Abstract

Nucleophilic substitution reactions of benzyl benzenesulphonates (YC₆H₄CH₂OSO₂C₆H₄Z) with anilines (XC₆H₄NH₂) have been studied in a series of methanol-acetonitrile mixtures. A more electron-donating substituent in the nucleophile (X =p-MeO) and a more electron-withdrawing substituent in the leaving group (Z =m-NO₂) led to an increase in the rate and to a later transition state with a longer substrate–leaving group bond and a shorter nucleophile–substrate bond. An electron-withdrawing substituent in the substrate (Y =p-Cl) was also found to favour a later transition state. An increase in the methanol content of the solvent increased reactivity but decreased selectivity in accordance with the reactivity–selectivity principle; however, the results of variations in the nucleophile, the leaving group, and the substrate in general violated the reactivity–selectivity principle. An MO model based on energy decomposition analysis for predicting S_N2 transition-state structure has been shown to apply to the results of this work.