The term has imprecisely been used to designate carboxylic
acyl carbenes
.
Keto
carbenes
are
carbenes
bearing an oxo function at an unspecified site.
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]