In electrophilic aromatic substitution, nitro groups direct new substituents to which position?

• A. Ortho
• B. Meta
• C. Para
• D. Any position

Answer: (B)

The directing outcome in electrophilic aromatic substitution is determined by the stability of the arenium ion (sigma complex) formed after the electrophile attaches. The nitro group strongly withdraws electron density from the ring by resonance (-M effect). In the sigma complex, placing the developing positive charge at positions ortho or para to the nitro group would place that positive charge adjacent to a strongly electron-withdrawing substituent, which destabilizes those intermediates. Substituting at the meta position avoids putting the positive charge next to the nitro group, leading to a more stable intermediate and making meta substitution the preferred pathway. Nitro groups are therefore meta-directors and also deactivating, slowing the reaction overall.