Hydrogen atom abstraction by radical cations. The reactions of 9-substituted acridine radical cations with cyclohexa-1,4-diene

Abstract

9-Substituted acridine radical cations undergo facile hydrogen atom abstraction reactions with cyclohexa-1,4-diene in dichloromethane–Bu₄NPF₆ (0.2 M). The kinetics of the reaction were studied by derivative cyclic voltammetry and observed to conform to the EC mechanism (charge transfer followed by irreversible first-order reaction). The products of the reactions are the protonated acridine substrate and dimer–substrate adducts of cyclohexa-1,4-diene. A comparison is made between the reactions of 9-phenylacridine and 9-phenylanthracene radical cations. The former undergoes rapid hydrogen atom abstractions, while the latter slowly dimerizes in the absence of nucleophiles. It is suggested that localization of the odd electron in a p-orbital on nitrogen imparts the hydrogen abstraction activity of the radical cation. Since there are no free p-orbitals on the carbon atoms of the aromatic rings in arene radical cations the hydrogen atom abstraction reaction pathway is not observed.