JEE Main · 2023 · 13 Apr 2023 · Shift 1 · Chemical Bonding and Molecular Structure

The dipole moment is largest when charge separation within the molecule produces aromatic stabilisation at both ends. In the cross-conjugated calicene skeleton, shifting the central $\pi$ bond makes the three-membered ring a cyclopropenyl cation with two $\pi$ electrons and the five-membered ring a cyclopentadienyl anion with six $\pi$ electrons. Both fragments satisfy the aromatic count, so this charge-separated form contributes strongly and creates a large permanent dipole. The compound built from the three- and five-membered rings therefore shows the highest dipole moment.