Platonic hydrocarbon

Platonic hydrocarbons are the molecular representation of platonic solid geometries with vertices replaced by carbon atoms and with edges replaced by chemical bonds. Not all platonic solids have a molecular counterpart:

* Tetravalent carbon excludes an icosahedron (5 edges meeting at each vertex) as a feasible objective;
* Angle strain prohibits an octahedron. Since 4 edges meet at each corner, there would be no hydrogen atoms, and this hypothetical octahedron molecule would be an allotrope C₆ of elemental carbon, not a hydrocarbon.

The following platonic hydrocarbons, on the other hand, have been synthesised:

* Tetrahedrane (C₄H₄) but only with proper substituents;
* Cubane (C₈H₈);
* Dodecahedrane (C₂₀H₂₀).

Note that with increasing number of carbon atoms in the frame, the geometry will eventually approximate a sphere. This is ultimately accomplished in fullerene although not a Platonic hydrocarbon itself (Buckminsterfullerene, C₆₀, has the shape of a truncated icosahedron, an Archimedean solid).

References

* Henning Hopf, "Classics in Hydrocarbon Chemistry", Wiley VCH, 2000.