Nucleophile and Aryl Radical Reactivity in SRN1 Aromatic Nucleophilic Substitution Reactions. Absolute and Relative Electrochemical Determination

Article abstract of DOI:10.1021/ja00298a009

Three electrochemical methods are used to obtain the rate of the Ar^.+Nu^- reaction.In the direct cyclic voltammetric method, the data are derived from the decrease of the substrate peak current upon addition of the nucleophile while in the relative method they are obtained from the peak heights of the two substitution products observed upon repetitive cycling of the substrate solution in the presence of two nucleophiles.In the redox catalysis method , the reduction of the substrate is catalyzed by an exogeneous reversible couple and the data are derived from the decrease of the catalytic current upon addition of the nucleophile.All three methods were combined to determine the reactivities of a series 26 aryl radical-nucleophile couples.In most cases, the rate constant is close to the diffusion limit.The exceptions concern the 2-quinolyl and 2-pyridyl radicals.The results are discussed in terms of energy difference between the ?* and ?* orbitals in the driving force of the reaction as related to characteristic standard potentials and bond energies.