Ring twisting in triphenylmethyl
The suggestion that triphenylmethyl has a "windmill" or propeller" shape was made by Lewis, Lipkin and Magel  who measured the UV absorption spectrum. The twisting is a compromise between the ortho-ortho steric repulsion involving aromatic hydrogens on adjacent rings and maximum resonance stabilization which favours a planar structure.
A gas phase electron diffraction study  and X-ray investigations of tris(p-nitrophenyl)methyl  and tris(3,5-di-tert-butylphenyl)methyl  suggest that the angle of twist is ca. 350.
ESR studies of 13C coupling constants indicate that twisting of the phenyl substituents also occurs in solution .
1. G.N. Lewis, D. Lipkin, and T.T. Magel, J. Amer. Chem. Soc., 1944, 66, 1579.
2. P. Anderson, Acta Chem. Scand., 1965, 19, 629.
3. P. Anderson and B. Klewe, Acta Chem. Scand., 1967, 21, 2599.
4. K. Schreiner, A. Berndt and F. Baer, Mol. Phys., 1973. 26, 929.
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