An obsolete term for @O04372@, based on the fact that compounds with a nitroso group, –N=O, bonded to a –CR2H group readily tautomerize to @O04372@.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1345 [Terms] [Paper]