Step 1: Recognizing the electrophilic substitution. Treating aniline with concentrated HNO₃/H₂SO₄ generates nitronium ions (NO₂⁺) that attack the aromatic ring in a typical electrophilic aromatic substitution. Step 2: Directing influence of –NH₂. The amino group powerfully activates the ring through resonance and steers incoming electrophiles to the ortho and para positions. Step 3: Product distribution. At 288 K, controlled mononitration yields both ortho-nitroaniline (P) and para-nitroaniline (Q). Step 4: Rationale for major isomer. The para position encounters less steric crowding than ortho, making p-nitroaniline the predominant product. Step 5: Negligible meta substitution. Meta attack is disfavored because the –NH₂ group stabilizes ortho/para Wheland intermediates through resonance, not the meta intermediate. Step 6: Conclusion. The reaction furnishes a mixture of o- and p-nitroaniline, with the para isomer as the major component.
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