Calicene, dipole moment

Calicene Dipole Moment (D) in Benzene Dipole Moment (D) in Dioxane Temp (X)... 

Calicene. like azulene (Problem 15.17), has an unusually large dipole moment for a hydrocarbon. Explain, using resonance structures. 

As with azulene, redistribution of the n electrons of calicene produces a resonance form in which both rings are aromatic and which has a dipole moment. 

Triafulvene ring systems capable of extended delocalization of charge (e.g. calicene 367) give spectral data fully compatible with highly dipolar character and many of these compounds possess significant dipole moments". ... 

The structures of several substituted methylenecyclopropenes and calicenes have been determined and reviewed . Of particular interest, however, is structural data of the parent hydrocarbon. The electric dipole moment (/i = 1.88 D) and the heavy atom molecular structure of methylenecyclopropene have been determined by microwave spectroscopy C=C, 1.323 A C-C, 1.441 A C=0, 1.212 A. The experimental and calculated structure... 

The dipolar property of calicenes is clearly shown by their large dipole moments (Table 1). ... 

Consider the case of triapentafulvalene (XIV) (calicene), a combination of tria-fulvene and pentafulvene. Hexaphenyltriapentafulvalene (XV) [37] was taken as a representative. This compound has the highest experimental dipole moment in the ground state ever recorded in a hydrocarbon - 6.3D (benzene, 30°C) [37]. A similar value was obtained in the case of the l,2-dimenthyl-3,4,5,6-tetraphenyl derivative [38]. 

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