Editing Allenes (section)

===Geometry===
[[File:Allene3D.png|thumb|right|3D view of propadiene (allene)]]
The central carbon atom of allenes forms two [[sigma bond]]s and two [[pi bond]]s. The central carbon atom is [[orbital hybridization#sp hybrids|sp-hybridized]], and the two terminal carbon atoms are [[orbital hybridization#sp2 hybrids|sp<sup>2</sup>-hybridized]]. The bond angle formed by the three carbon atoms is 180°, indicating linear geometry for the central carbon atom. The two terminal carbon atoms are planar, and these planes are twisted 90° from each other. The structure can also be viewed as an "extended tetrahedral" with a similar shape to [[methane]], an analogy that is continued into the stereochemical analysis of certain derivative molecules.