Editing Allenes (section)

{{Short description|1=Any organic compound containing a C=C=C group}}
{{for|the given name|Allene (given name)}}
{{For|the organic compound with the common name allene|Propadiene}}
[[File:Propadiene structure.svg|right|thumb|[[Propadiene]], the simplest allene, is also known as allene]]

In [[organic chemistry]], '''allenes''' are [[organic compounds]] in which one [[carbon]] atom has [[double bond]]s with each of its two adjacent carbon atoms ({{chem2|R2C\dC\dCR2}}, where R is [[hydrogen|H]] or some [[organyl group]]).<ref>{{GoldBookRef|title=allenes|file=A00238}}</ref> Allenes are classified as [[diene#Classes|cumulated dienes]]. The parent compound of this class is [[propadiene]] ({{chem2|H2C\dC\dCH2}}), which is itself also called ''allene''. A group of the structure {{chem2|R2C\dC\dCR\s}} is called '''allenyl''', while a substituent attached to an allene is referred to as an '''allenic''' substituent (R is H or some alkyl group). In analogy to [[Allyl group|allylic]] and [[Propargyl group|propargylic]], a substituent attached to a saturated carbon α (i.e., directly adjacent) to an allene is referred to as an '''allenylic''' substituent.  While allenes have two consecutive ('cumulated') double bonds, compounds with three or more cumulated double bonds are called [[cumulene]]s.