ketenes

https://doi.org/10.1351/goldbook.K03378
Compounds in which a carbonyl group is connected by a double bond to an alkylidene group R2C=C=O .
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]