Cumulenes in which one or more carbon atoms of the cumulative bond system have been replaced
by heteroatoms. E.g.
O=C=C=C=O, but not
CH2=C=O, ketene, nor
O=C=O,
carbon dioxide, which are heteroallenes.
Source:
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on
structure (IUPAC Recommendations 1995))
on page 1340