acyl carbenes 

https://doi.org/10.1351/goldbook.A00121
Any compound . In organic chemistry, an unspecified acyl carbene is commonly a carboxylic acyl carbene, .
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1311 [Terms] [Paper]