carbenes 

https://doi.org/10.1351/goldbook.C00806
The electrically neutral species H2C: and its derivatives, in which the carbon is covalently bonded to two univalent groups of any kind or a divalent group and bears two nonbonding electrons, which may be spin-paired (singlet state) or spin-non-paired (triplet state). In systematic name formation, carbene is the name of the parent hydride :CH2 hence, the name dichlorocarbene for :CCl2. However, names for acyclic and cyclic hydrocarbons containing one or more divalent carbon atoms are derived from the name of the corresponding all-λ4-hydrocarbon using the suffix -ylidene. E.g. prop-2-en-1-ylidene, H2C=CHCH: ethenylidene, H2C=C:; cyclohexylidene,

Subclasses of carbenes include acyl carbenes , imidoyl carbenes, and vinyl carbenes.
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1324 [Terms] [Paper]
See also:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1092 [Terms] [Paper]
Citation: 'carbenes' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C00806 RIS BibTex EndNote
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Last revised: February 24, 2014