QuestionOrganic / dipole moment and aromaticity
Which molecule in each of the following pairs has a higher dipole moment?
- (a) 1 and 3
- (b) 1 and 4
- (c) 2 and 3
- (d) 2 and 4
Answer: (b) 1 and 4
Pair X: 1 cyclopropenone — C=O polarises to give an aromatic 2π cyclopropenium ring → large dipole (> 4 D); 2 (cyclopropanone) cannot. Pair Y: 4 (calicene-type sesquifulvalene) separates charge into tropylium⁺ (6π) and cyclopentadienide⁻ (6π), both aromatic → larger dipole. → 1 and 4 → (b).