# Why isn't allene planar?

A simplified explanation is that the central carbon atom's ${p}_{x}$ and ${p}_{y}$ orbitals are aligned to make perpendicular $\pi$ bonds, corresponding to perpendicular ${\text{CH}}_{2}$ groups. The same $p$ orbital cannot (easily) make two parallel $\pi$ bonds on either side, especially if they both contain localized electrons.