Cyclic hemiacetals formed by intramolecular addition of a hydroxy group to an aldehydic or ketonic carbonyl group. They are thus 1-oxacy-cycloalkan-2-ols or unsaturated analogues, e.g.
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[obsolete] This term has also been used for hydroxy lactones, but such use is not recommended.
Source: PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1347 (https://doi.org/10.1351/pac199567081307)