Triphenylene, structure

Polymers 340-343 have a deep red or brown color probably related to the presence of conjugated polynuclear units. A similar color was noted in the polymers derived from cation-radical polymerization of 1,1 -binaphthyl and o-terphenyl. In these cases the color was attributed to the presence of cation-radicals of perylene and triphenylene structural units [193,201,203]. Perylene units are possible in polymers 340-343 (Fig. 46). 

Under oxidation conditions (electrochem. or chem.), starting from substituted benzenes or derivatives, triphenylene structures (benzo[l,2 3,4 5,6]tris[arylenes] are formed, e.g. ... 

Bond angle/bond length relationships do not readily account for the bond localization noted for starphenylene (116) and triphenylene (124). A cursory examination of the structures reveals that in these cases the annelated cycles can have an aromatic character of their own. In staiphenylene the cycle would contain four electrons and be antiaromatic, whereas in triphenylene the cycle would have six electrons and be aromatic. From the simple Huckel rule, the antiaromatic cycle should be disfavored. In such a case, structural stabilization can be accomplished by greater contribution from the resonance form that has single-bond character at the endo-honA. The reverse is expected for the aromatic cycle. This model is simple, predictive, and accurate ... 

The presence of overcrowding in triphenylene has been demonstrated by Clar (1950) from an examination of the absorption spectra at 18°C and — 170°C. At — 170°C the / -band spectra of such aromatic hydrocarbons as benzene, naphthalene, anthracene, and pyrene become more distinct, showing much more fine structure than at 18°C. This is explained by the cessation at low temperature of thermal collisions which produce molecular deformations, thereby improving the definition of the molecular electronic orbitals. Where this change in spectra does not occur, permanent deformation at both low and high temperatures... 

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