vinyl carbenes

https://doi.org/10.1351/goldbook.V06620
Carbenes having a vinylic group on a carbenic carbon atom $\ce{R2C=CRC{:}R <-> R2C^{+}–CR=C^{−}R}$. E.g. $\ce{H2C=CHC{:}H}$, prop-2-en-1-ylidene.
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1374 [Terms] [Paper]