SOLVENT EFFECTS ON THE REACTIVITY OF SOLVATED ELECTRONS WITH CHARGED SOLUTES IN METHANOL WATER AND ETHANOL WATER MIXED-SOLVENTS

Reactivities of the anions NO3- and CrO42- with es- are more sensitive to solvent composition than are those of the cations Ag+ and Cu2+. After accounting for the effect of the Coulombic interaction on the probability of approach of es- and a reactant ion to within the reaction radius R, we find that the value of R increases with increasing Coulombic repulsion between the reactants and decreases with increasing Coulombic attraction between the reactants. The solvent dependence of k2(es- + Ag+) is similar to that of k2(es- + nitrobenzene). In the water-rich region (mole fraction water 1 > χw > χηmax) the rate constants conform approximately to the Smoluchowski-Stokes-Debye relation. In the region χw < χηmax the rate constants do not conform to this relation; the change is attributed to a change in the packing of solvent molecules about the reactants in a manner that affects their reactivities and diffusivities. The reaction es- + NO3- is particularly sensitive to the nature of the solvent; it is least efficient in pure methanol, where it has a very large, negative entropy of activation. © 1990 American Chemical Society.