Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
The compound exhibits a large dipole moment. Which of the following resonance structures adequately explain this observation? (i) (ii) (iii) (iv)
Options
- A(ii) and (iii)
- B(iv) only
- C(i) only
- D(iii) and (iv)
Correct answer
D. (iii) and (iv)
Step-by-step solution
The given molecule consists of a cyclopentadiene ring and a cyclopropene ring connected by a double bond. To explain the large dipole moment, we must look for a highly stable zwitterionic (charge-separated) resonance structure. We can polarize the central double bond in two ways: 1. If the electrons shift towards the three-membered ring, the cyclopropene ring gains a negative charge (cyclopropenyl anion, 4 electrons, anti-aromatic) and the cyclopentadiene ring gains a positive charge (cyclopentadienyl cation, 4 ele