cumulenes

https://doi.org/10.1351/goldbook.C01440
@H02889@ (and by extension, derivatives formed by substitution) having three or more @C01437@, e.g. R2C=C=C=CR2.
See also:
allenes
,
heterocumulenes
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1329 [Terms] [Paper]