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

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 SN2 transition-state structure has been shown to apply to the results of this work.