Hydrogen transfer in protic solvents

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In chemistry, autoprotolysis is a molecular autoionization, a chemical reaction in which a proton is transferred between two identical molecules, one of which acts as a Brønsted acid, releasing a proton that is accepted by the other molecule, which acts as a Brønsted base.^[1] Any chemical that contains both acidic hydrogen and lone pairs of electrons to accept H⁺ can undergo autoprotolysis.

For example, water undergoes autoprotolysis in the self-ionization of water reaction.

2 H₂O ⇌ OH⁻ + H₃O⁺

For example, ammonia in its purest form may undergo autoprotolysis:

2 NH₃ ⇌ NH−2 + NH+4

Another example is acetic acid:

2 CH₃COOH ⇌ CH₃COO⁻ + CH₃COOH+2

A lyate ion is the anion derived by the deprotonation of a solvent molecule.^[2] For example, a hydroxide ion is formed by the deprotonation of water, and methoxide (CH₃O⁻) is the anion formed by the deprotonation of methanol. Its counterpart is a lyonium ion, the cation derived by the protonation of a solvent molecule.^[3] For example, a hydronium ion is formed by the protonation of water, and CH₃OH+2 is the cation formed by the protonation of methanol.

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

• Onium ion, a protonated molecule more generally
• Ion transport number
• Ionic atmosphere