Hexa phenylethane

A close analogy to the carbon radicles is provided by certain nitrogen compounds, which are likewise free unsaturated complexes partaking of the character of atoms and having an abnormal valency. With nitrogen, as with carbon, the existence of radicles also depends on the presence of aromatic rings. Tetraphenylhydrazine corresponds to hexa-phenylethane. 

However, if positive substituents are introduced into the benzene rings, hydrazine derivatives result which considerably surpass hexa-phenylethane in their degree of dissociation. Already the colourless p-tetra-anisylhydrazine is appreciably dissociated at room temperature into the green p-dianisylnitrogen radicles (H3CO.C6H4)2N and the corre-... 

It has been pointed out by Adrian81 that there is steric hindrance in the triphenylmethyl radical, the phenyl groups being twisted about the bond to the central atom through about 32°. This twist decreases the calculated resonance energy from 35 kcal/mole (for planarity) to 21 kcal/mole. The steric repulsion energy of the two halves of hexa-phenylethane is estimated to be about 36 kcal/mole, and the enthalpy of dissociation is about 16.5 kcal/mole. 

Free radicals. Evidence for the existence of free radicals came in 1900 from Gomberg, who showed that hexa-phenylethane in benzene solution dissociates spontaneously into a free triphenyl methyl radical... 

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