Carbenes $\ce{R2C{:}}$ formed by mono or dialkyl substitution of
methylene, $\ce{H2C{:}}$, e.g. $\ce{CH3CH2CH{:}}$ propylidene.
Source: PAC, 1995,
67, 1307. (
Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1314 [
Terms] [
Paper]