Solvent and ion pairing effects on the reaction entropy for the electroreduction of aromatic molecules

Abstract

The reaction entropy, Δ S o r, for the electroreduction of p-dicyanobenzene, anthracene and nitromesitylene has been measured in a number of solvents using a non-isothermal cell. The solvent effect on the values of Δ S o r has been discussed in terms of the Born dielectric continuum model and the specific solvation given by the solvent parameters of Lewis acidity and basicity. A correlation between the solvent acceptor number and Δ S o r values is observed in the case of p-dicyanobenzene radical anions with a localized charge at the cyano groups, whereas the dielectric approach is more important for anthracene radicals with a stronger charge delocalization when the specific solvation is much weaker. A two-parameter correlation with acceptor and donor numbers has been observed for the Δ S o r values of nitromesitylene where association between the radical anions and electrolyte cations occurs. An increase in the Δ S o r values for the reduction of o-naphthoquinone in dimethylsulphoxide with an increase in the association constant for a series of cations has been found.