https://doi.org/10.1351/goldbook.12734
Structural isomer that can readily convert to another form that differs only by the attachment position of a hydrogen atom and the location of double bond(s).
Note: In most cases, these isomers are formed by a proton shift to or from heteroatoms such as \(\ce{O}\), \(\ce{N}\), or \(\ce{S}\) as typified by the enol and keto forms of carbonyl compounds. Tautomers rapidly interconvert by proton transfer and are usually in equilibrium with one another.