Applicability of the Brønsted Relation to Reactions of the Hydrated Electron

The hydrated electron, e−aq, reacts with Brønsted acids, BH+, to yield H atoms through a process of proton transfer magnified image For a series of Brønsted acids of charge types 1+, 0 and 1−, the rate constant, k, is related to the acid dissociation constant K according to k/p = GA(qK/p)α, where α = 0.42. Some acids give rate constants deviating from this relation. These are shown to be ambident reagents with e−aq, one pathway obeying the Brønsted relation, while the other may be nucleophilic addition of e−aq to a reaction center in B. Thus —k(e−aq), the rate of disappearance of e−aq may be greater than +k(H), the rate of formation of H atoms. To account for the results, a molecular model for the structure of e−aq forming a hydrated anion is favored. Its reaction with H+aq is discussed, accounting for recent observations on the rate of the reaction e−aq + H+aq → Haq, which in our view corresponds to proton transfer to fully ordered hydrated electrons, rather than electron addition to H+aq.