Question

In electrophilic aromatic substitution reaction, the nitro group is meta directing because it:

• A. decreases electron density at ortho and para positions
• B. decreases electron density at meta position
• C. increases electron density at meta position
• D. increases electron density at ortho and para position

Hint:

Electron-withdrawing groups having (-M) effect (like (-textNO2), (-textCN), (-textCOOH)) are deactivating and meta-directing in electrophilic aromatic substitution reactions.

Answer 1

The Correct Option is A

Step 1: Nature of the nitro group (\(-\text{NO}_2\)). The nitro group is a strong electron-withdrawing group due to:

\(-I\) (inductive) effect
\(-M\) (mesomeric or resonance) effect
Step 2: Effect of resonance on electron density. In resonance structures of nitrobenzene, the electron density is withdrawn from the benzene ring, particularly from the ortho and para positions, making them electron deficient. Step 3: Stability of the sigma complex. During electrophilic substitution:

Ortho and para sigma complexes are highly destabilized due to positive charge near the electron-withdrawing nitro group.
Meta substitution avoids this destabilization.
Step 4: Final conclusion. Since the nitro group decreases electron density at ortho and para positions, substitution occurs preferentially at the meta position.