The Triphenylmethyl Radical, Hexaphenylethane, and Gomberg's Hydrocarbon

Pages 926-927

When the triphenylmethyl radical dimerizes, it does not form hexaphenylethane because of the large amount of steric strain that would be present in this compound. Instead, the radical bonds to the much less sterically hindered para position of a ring in another radical, even though this results in the loss of aromatic stabilization in this ring.

	The Triphenylmethyl Radical For maximum resonance stabilization, the triphenylmethyl radical would like to be planar. However, this causes significant steric strain because the hydrogens in the ortho positions of the benzene rings would be forced into close proximity. Therefore, the radical actually is shaped like a propeller. The carbon bonded to the three benzene rings is red in this model.
	Hexaphenylethane This compound has a large amount of steric strain and does not form from the coupling of two triphenylmethyl radicals. The two ethane C's are red.
	Gomberg's Hydrocarbon The coupling of the methyl C (red) of one triphenylmethyl radical at the para position of one ring of a second triphrenylmethyl radical results in the formation of Gomberg's hydrocarbon. (The original methyl C of the second triphenylmethyl radical is green.) Even though the aromatic stabilization of one ring is lost, this compound is more stable than hexaphenylmethane because it has less steric strain.