Electron transfer processes equilibrium electrostatics

The microscopic mechanism of these reactions is closely related to interaction of the reactants with the medium. When the medium is polar (e.g., water), this interaction is primarily of electrostatic nature. The ionic cores of the donor and acceptor located at fixed spatial points in the medium produce an average equilibrium polarization of the medium, which remains unchanged in the course of the reaction and does not affect the process of electron transfer itself. The presence of the transferable electron in the donor induces additional polarization of the solvent around the donor that is, however, different from polarization in the final state where the electron is located in the acceptor. 

The reduction process of polycycles by lithium metal converts the neutral atoms to anions. The electron transfer is best achieved in ethereal solvents. This enables the stabilization of the lithium cation by coordination to the oxygen atoms of the solvent. The hydrocarbon anion and the cation are linked together by electrostatic forces in which the solvent molecules are also involved, therefore the ion-solvation equilibrium should be considered8. The limiting cases in this equilibrium are free ions and contact ion-pairs (CIP), and in between there are several forms of solvent separated ion-pairs (SSIP)9. In reality, anionic species of aromatic hydrocarbons in ethereal solvents exist between CIP and SSIP. Four major factors influence the ion-solvation equilibrium of lithium-reduced 7T-conjugated hydrocarbons, as observed by H and 7Li NMR spectroscopies8,10. 

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