New Insights into the Substituents’ Effect on the Formation and Dissociation of Radical Anions: Dissociative Electron Transfer to Arylsulfonylphthalimides

Abstract

AbstractThe electrochemical reduction of a series of biologically relevant p‐substituted arylsulfonylphthalimides was investigated and the results were analysed using theoretical calculations and application of Savéant's dissociative electron transfer theory. The dissociation rate constants of the radical anion intermediates were calculated and showed that upon changing the substituent from the MeO, to Me, H, F, Cl and CN the dissociation became faster. A good correlation with the Hammett substituent constants was also obtained. With the NO2 substituent the trend was however inversed. These results and the electrolysis data showed that the dissociation involves the N−S chemical bond. Theoretical calculations showed that for all investigated compounds the extra electron was hosted by the phthalimidyl group except for the p‐NO2 substituted compound for which the extra electron was hosted by the nitrophenyl moiety. Thermodynamic considerations showed that the dissociation of the radical anion of the p‐NO2 compound followed a heterolytic cleavage whereas those of the rest of the investigated compounds followed a homolytic cleavage. The above intriguing result was rationalized through application of the extension of Savéant's dissociative electron transfer theory to the decomposition of radical anions. This study is important not only for understanding substituents’ effect on the biological activity of these compounds but also on the formation and dissociation of radical anions in general.