Question

The presence of –NO$_2$ group at ortho or para position increases the reactivity of haloarenes towards nucleophilic substitution reactions. Give reason to explain the above statement.

Hint:

The electron-withdrawing –NO$_2$ group makes the carbon attached to the halogen more electrophilic, thus facilitating nucleophilic substitution at the ortho and para positions.

Answer 1

The presence of the electron-withdrawing –NO$_2$ group at the ortho or para positions of a halogenated benzene ring increases the reactivity of haloarenes towards nucleophilic substitution reactions. This is because:
- The –NO$_2$ group is electron-withdrawing, meaning it pulls electron density away from the benzene ring through the inductive effect.
- This increases the partial positive charge on the carbon atom attached to the halogen (which is the site of nucleophilic attack).
- The increased positive charge on the carbon makes it more electrophilic, thus more susceptible to attack by nucleophiles, thereby increasing the rate of nucleophilic substitution reactions.

Step 1: The electron-withdrawing nature of the –NO$_2$ group enhances the electrophilicity of the carbon bonded to the halogen.


Step 2: The nucleophile can more easily attack this carbon, especially at the ortho and para positions, where the electron-withdrawing effect of the NO$_2$ group is strongest.