Isomerism of the general form:
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
electrofuge or
nucleofuge during
isomerization. The commonest case, when the
electrofuge is
H+, is also known as '
prototropy'. Examples, written so as to illustrate the general pattern given above, include:
Keto-enol tautomerism, such as:
The grouping Y may itself be a three-atom (or five-atom) chain extending the
conjugation, as in:
The double bond between Y and Z may be replaced by a ring, when the phenomenon is
called ring-chain tautomerism, as in:
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1171
