Consider the following cross-conjugated and related molecules: (I) Fulvalene (a system of two cross-conjugated five-membered rings) (II) Sesquifulvalene (a system of a five-membered and a seven-membered cross-conjugated ring) (III) Heptafulvalene (a system of two cross-conjugated seven-membered rings) (IV) Bicyclohexylidene (two six-membered saturated rings connected by a double bond) Which of these molecules is expe

Step-by-step solution

A high permanent dipole moment in a hydrocarbon arises when a dipolar resonance contributor is exceptionally stable. For sesquifulvalene (II), heterolytic polarization of the central exocyclic double bond can place a negative charge on the five-membered ring and a positive charge on the seven-membered ring. This results in a cyclopentadienyl anion (6 electrons, aromatic) and a cycloheptatrienyl (tropylium) cation (6 electrons, aromatic). Since both rings become aromatic, this dipolar structure is highly stable and