Electron Affinities of Quinones : Correlation of One-electron Redox Potentials with Quantum-mechanical Calculation

Abstract

IN 1949, Maccoll¹ showed that a linear relationship existed between the energy of the lowest unoccupied molecular orbitals of aromatic hydrocarbons (their electron affinities) and their polarographic half-wave potentials (E_½). This relationship was further discussed and extended by Pullman et al.² and Hoijtink³, although it was not always appreciated at that time that strictly only those E_½ values obtained under conditions such that the reversible addition of one electron only (R + e ↔ R⁻) is involved should be considered⁴; the potential is then virtually the standard potential for a one-electron addition. It has been suggested⁴ that such measurements for other aromatic molecules might provide equally valid parameters for certain properties, such as electron affinity, for which few independent estimates exist, and recently some E_½ values of well-known electron acceptors were given with an indication of their possible application to charge-transfer studies⁵.