Pyridone may refer to several organic compounds with the formula C5H4NH(O): These can adopt three tautomers, a oxo form, a zwitterion form, and a enol form.
Whereas 2-pyridone (α) and 4-pyridone (γ) predominantly adopt the oxo form, the 3-pyridone (β) cannot, and instead adopts an equilibrium of the zwitterion form, pyridin-1-ium-3-olate, and the enol form, 3-hydroxypyridine (the canonical form).
The 3-pyridone is not mesoionic.
This property of 3-hydroxypyridine is leveraged in biology in pyridoxal phosphate: this common cofactor that catalyses a variety of reactions thanks to a stable cationic form.