Which one of the following isomeric compounds has the gretest dipole moment?

Options

A.
B.
C.
D.

Answer

C

Explanation

Although neither the cycloheptatriene nor the cyclopentadiene ring alone is aromatic, charged resonance structures show a predominance of `-ve` charge in the 5-memebered ring making it similar to the aromatic cyclopentadienyl anion. In these structures the 7-membered ring bears a positive charge, giving it the aromatic character of the cycloheptatrienyl cation: The resonance hybrid is The main contributing structures to the hybrid show charge separation responsible for the observed dipole moment.