Tautomeric forms of @L03435@, having an endocyclic carbon-nitrogen double bond. Thus, cyclic carbox@I02949@, e.g.
L03437.png
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1346 [Terms] [Paper]