Structure and dynamics of OH ^- (aq)

Topological defects in aqueous solution in the form of H ⁺(aq) and OH ^-(aq) ions undergo anomalously fast transport via the structural Grotthuss diffusion mechanism. However, while the microscopic details of this process are well understood for H ⁺(aq), the corresponding picture for OH ^-(aq) remains unresolved. Mechanistic scenarios proposed previously are critically reviewed with the help of the presolvation concept, which provides a unifying framework for understanding charge migration mechanisms in hydrogen-bonded networks. It is argued that OH ^-(aq) features a nonclassical, in the Lewis sense, hypercoordinated solvation structure. The resulting mechanism deviates substantially from the traditional "mirror image" picture. Within the presolvation concept, it can also be suggested why alternative scenarios are inconsistent with experimental data.