Predict the % of nitration products when aniline is subjected to nitration with Conc. $HNO_3$/Conc. $H_2SO_4$.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → o-nitroaniline 2%; m-nitroaniline 47%; p-nitroaniline 51%
When aniline is subjected to nitration using concentrated nitric acid and concentrated sulfuric acid, the major products are meta (47%) and para (51%), while ortho is very less (2%).
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In strongly acidic medium (conc. HNO₃ / conc. H₂SO₄), aniline gets protonated to form the anilinium ion (–NH₃⁺).
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This group is electron-withdrawing and deactivating, and it acts as a meta-directing group.
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Hence, meta substitution becomes significant (~47%).
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However, a small amount of free (unprotonated) aniline still exists, which is ortho/para directing:
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Para product is favored due to less steric hindrance → 51%
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Ortho is very less due to steric hindrance → 2%
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Key idea
Strong acidic medium → –NH₂ becomes –NH₃⁺ → meta directing dominates, but para still major due to steric + partial free base
To memorise
In strong acidic conditions, aniline behaves as a meta director; otherwise, it is an ortho/para director.Trick line: “Acid bana de meta, free amine de ortho-para.”