In acid–base chemistry, homoassociation (an IUPAC term)[2] is an association between a base and its conjugate acid through a hydrogen bond.
This effect arises from the stabilization of the conjugate base by its formation of a hydrogen bond to the parent acid.
A well known case is hydrofluoric acid, which is a significantly stronger acid when concentrated than when dilute due to the following equilibria: Overall: The bifluoride anion (HF2−) encourages the ionization of HF by stabilizing the F−.
The effect of homoassociation is often high in nonaqueous solutions, wherein dissociation is often low.
Carboxylic acids and phenols exhibit this effect,[3] for example in sodium diacetate.