In the context of nucleophilic aromatic substitution, why is the ${\mathrm{NO}}_2$ group considered a meta director when it comes to electrophilic aromatic substitution reactions?

• A. Because the ${\mathrm{NO}}_2$ group increases electron density at all positions equally, so substitution occurs randomly.
• B. Because the ${\mathrm{NO}}_2$ group stabilizes carbocation intermediates at the ortho and para positions, favoring meta substitution.
• C. Because the ${\mathrm{NO}}_2$ group withdraws electron density from the ortho and para positions through resonance and inductive effects, making the meta position relatively more reactive toward electrophiles.
• D. Because the ${\mathrm{NO}}_2$ group donates electron density to the ortho and para positions, making the meta position less reactive toward electrophiles.

Answer: (C)

Verified step by step guidance

1. Understand that electrophilic aromatic substitution (EAS) involves the attack of an electrophile on the aromatic ring, forming a positively charged carbocation intermediate (the sigma complex or arenium ion).
2. Recognize that substituents on the aromatic ring influence the electron density distribution through resonance and inductive effects, which affects the stability of the carbocation intermediate formed during EAS.
3. Know that the nitro group (\$\mathrm{NO_2}\$) is a strong electron-withdrawing group due to its resonance and inductive effects, which pull electron density away from the aromatic ring, especially at the ortho and para positions.
4. Because the \$\mathrm{NO_2}\$ group withdraws electron density from the ortho and para positions, the carbocation intermediates formed at these positions are less stabilized, making these positions less favorable for electrophilic attack.
5. Consequently, the meta position becomes relatively more electron-rich and more reactive toward electrophiles, which is why the \$\mathrm{NO_2}\$ group directs electrophilic substitution to the meta position, classifying it as a meta director.