Symmetry Lab › D2d › Allene (propadiene)
C₃H₄ Allene (propadiene)
Two perpendicular CH₂ planes · point group D2d · order 8
- Point group
- D2d — A C2 principal axis, 2 perpendicular C2 axes and 2 dihedral mirror planes that bisect them; the principal axis is also an S4 axis.
- Order
- 8
- Operations
- E, 2S₄, C₂, 2C₂′, 2σd
- Shape
- Two perpendicular CH₂ planes
- Atoms
- 7 (C × 3, H × 4)
Symmetry elements of C₃H₄
- C₂ — along the C=C=C axis
- S₄ — rotate 90° about the axis, then reflect: swaps the two CH₂ groups
- C₂′ (1) — perpendicular to the axis, between the two CH₂ planes
- C₂′ (2) — perpendicular to the axis, between the two CH₂ planes
- σd (1) — the plane of one CH₂ group
- σd (2) — the plane of the other CH₂ group
Structure
- C=C 1.308 Å, C–H 1.087 Å
- H–C–H 118.2°
- The two CH₂ groups lie in perpendicular planes
