Question

Which of the following will have the least dipole moment?

• A. I
• B. II
• C. III
• D. Both (I) and (II)

Answer 1

The correct option is C III

In ionic form of compound (I), both rings are aromatic in nature with 6 and 2 $\pi$-electrons. Hence, the ionic form will be more stable and have more dipole moment.
In ionic form of compound (II), again both rings are aromatic in nature with 6$\pi$- electrons. Hence, the ionic form will be more stable and have more dipole moment.
In ionic form of compound (III), one ring is aromatic with 6$\pi$- electron and other ring is antiaromatic with 4$\pi$-electrons. This will destabilise the ionic form of the compound. Hence, its dipole moment will be comparitively lower than (I) and (II).