Consistent theoretical treatment of degenerate electron exchange reaction in the liquid phase within the framework of the encounter theory has been performed. Finite duration of the reactant encounter and reaction reversibility have been taken into account. Applicability range of the widely used phenomenological approach has been established, encounter theory equations for the radical ions having large hyperfine couplings have been obtained. Case of a radical ion with one magnetic nucleus has been studied in detail. Theoretical treatment of degenerate electron exchange reaction within the framework of the semiclassical approximation corresponding to a large number of magnetic nuclei has been carried out.