Question

Calicene, like azulene (Problem 15-17), has an unusually large dipole moment for a hydrocarbon. Explain, using resonance structures.

Answer 1

Answer:-

​​​​​Calicene is a hydrocarbon of fulvalene class and consists of a cyclopentadiene ring bonded with a cyclopropene ring. It has a large dipole moment of 4.66 D

The Concepts:

1) According to Huckel rule, a molecule is said to be aromatic if:

a) it is cyclic.

b) it is conjugated and coplanar.

c) it contains (4n + 2) pi-electrons.

2) Dipole = q × l

Where, q = charge and l = length of bond.

In other words, we can say that a dipole is a polar bond consisting of separated positively and negatively charged ends.

"Explaination":-

The calicene has a unusally large dipole moment because of the charge separation in the resonance structures of the molecule. Due to charge separation , both rings in calicene acquire aromatic character. Thus, the charged resonance structures are important contributor of resonance hybrid.

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