The Structure of the H₃O⁺ Hydronium Ion in Benzene

Infrared, X-ray structural, ¹H NMR, and computational evidence for π-solvation of H₃O⁺ by benzene molecules is presented. A salt with a discrete [H₃O·3benzene]⁺ cation can be isolated using a very weakly interacting carborane counterion, CHB₁₁Cl₁₁^-. π-Arene solvation of H₃O⁺ explains the solubility of this salt in benzene solution. Similar results are indicated for the “Zundel-type” H₅O₂⁺ ion. These findings suggest structures for the active protonating species when strong acids are used as catalysts in arene solvents containing trace water. They are also relevant to structures that may be present in biological proton transport.