Bo Svensmark Jensen

Reversible anion radical–dianion redox equilibria involving ions of simple aromatic compounds

Anthracene, benzophenone, nitrobenzene, and several other simple aromatic compounds undergo two consecutive reversible one-electron transfers to give first the anion radical and then the dianion, both species being stable during the time scale of cyclic voltammetry in several electrophile-free solvents.

On the origin of voltammetric pre-peaks and cathodic potential shifts during anodic substitution reactions

Abstract During voltammetric pyridination of 9-phenylanthracene a pre-peak was observed, the height of which was in direct relation to the stoichiometric ratio of 9-phenylanthracene and pyridine. In order to determine whether or not the latter result could be taken as evidence for a nucleophile assisted electron transfer, a “non-assisted” mechanism was simulated. It was found that an ecec mechanism gave substantial cathodic shifts of the peak potential for oxidation of a substrate in presence of a reactant, and if the rate constants were sufficiently high not only a cathodic shift, but also a pre-peak was observed during simulation. Thus, the experimental observations cannot be used as evidence for an assisted mechanism.

Solvent effect on the disproportionation of the tetrakis-p-methoxyphenylethylene cation radical. An experimental verification of theory

The disproportionation equilibrium, 2 TME+˙ [graphic omitted] TME2++ TME, where TME is tetrakis-p-methoxyphenylethylene, was observed to be profoundly influenced by the fraction of acetonitrile present in dichloromethane–acetonitrile mixtures. In going from pure acetonitrile to pure dichloromethane, K decreased from 1·1 to 0·03. In the mixed solvent system, peak voltammograms show increasing peak width with increasing fraction of dichloromethane. Differences in E0 for the two charge transfers were estimated from the voltammetric peak widths and disproportionation equilibrium constants were calculated. The plot of log K versus% acetonitrile was found to be linear over the entire range of solvent composition. Both the cation radical and dication were found to be stable in the solvent mixtures which had been passed over neutral alumina. Disproportionation equilibrium constants calculated from the visible absorption spectra of partially oxidized solutions of TME were nearly identical with the values predicted from analysis of the voltammetric peak widths.