tautomerism

https://doi.org/10.1351/goldbook.T06252
@I03294@ of the general form:
T06252-1.png
where the isomers (called tautomers) are readily interconvertible; the atoms connecting the groups X, Y, Z are typically any of C, H, O or S, and G is a group which becomes an @E01965@ or @N04246@ during @I03295@. The commonest case, when the @E01965@ is H+, is also known as 'prototropy'. Examples, written so as to illustrate the general pattern given above, include: @K03382@-enol tautomerism, such as:
T06252-2.png
T06252-3.png
The grouping Y may itself be a three-atom (or five-atom) chain extending the @C01267@, as in:
T06252-4.png
The double bond between Y and Z may be replaced by a ring, when the phenomenon is called ring-chain tautomerism, as in:
T06252-5.png
See also:
ambident
,
sigmatropic rearrangement
,
tautomerization
,
valence tautomerization
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1171 [Terms] [Paper]