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).

• 
  Tetrahedrane
• 
  Cubane
• 
  Dodecahedrane

References

• Henning Hopf, Classics in Hydrocarbon Chemistry, Wiley VCH, 2000.