Question

Which one of the following is most stable?

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

All are carbanions. For stability, we should look at the molecule that has the greatest distribution of electrons - how the charge is spread across multiple atoms of the molecules. The more diffused the charge distribution, the more stable the carbanion. From the given options, we have $Cl$ and $N{O}_2$ groups which are deactivating. But the chlorine group also increases the charge density via conjugation. That leaves us with the nitro group which is electron-withdrawing by both inductive and conjugation effects. The conjugation is much more pronounced and the $–R$ effect increases the stability of carbanion.