What is the point group of Allene?

Allene (C4H4) belongs to the D2h point group. This is due to its unique molecular geometry, which features a central carbon atom bonded to two other carbon atoms, with each of those bonded to two hydrogen atoms. The symmetry elements present include a principal rotation axis (C2), two perpendicular C2 axes, and horizontal and vertical mirror planes (σh and σv). This combination of symmetry elements classifies allene within the D2h point group.