In chemistry, a lyonium ion is the cation derived by the protonation of a solvent molecule.[1] For example, a hydronium ion is formed by the protonation of water, and CH3OH+2 is the cation formed by the protonation of methanol.

Its counterpart is a lyate ion, the anion formed by the deprotonation of a solvent molecule.

Lyonium and lyate ions, resulting from molecular autoionization, contribute to the molar conductivity of protolytic solvents.


Lyate ion Original solvent Lyonium ion
name formula name formula name formula
Fluoride F Hydrogen fluoride HF Fluoronium H2F+
Hydroxide HO Water H2O Hydronium H3O+
Azanide NH2 Ammonia NH3 Ammonium NH+4
Methanide CH3 Methane CH4 Methanium CH+5
Methoxide CH3O Methanol CH4O Methyloxonium CH5O+

See also