Nucleophilic character of acyl radicals. Substituent effects on the homolytic acylation of protonated heteroaromatic bases

Abstract

The relative rates of the homolytic acylation of protonated 2- and 4-substituted quinolines with acetyl and benzoyl radicals are reported. Orientation of products and reactivity show clear-cut nucleophilic character for the acyl radicals. The relative rates have not been correlated with the Hammett σm constants because of enhanced conjugation of the electron-releasing substituents. A much smaller effect is observed for substituted benzoyl radicals; in this case a Hammett correlation gives ρ=–0·49.