Question: Aniline on direct nitration yields:

Step 1 (Governing Principle & Reaction Context): [0.25 Mark]

Direct nitration of aniline ($C_6H_5NH_2$) using concentrated $HNO_3$ and $H_2SO_4$ (nitrating mixture) results in the protonation of the amino group to form the anilinium ion ($C_6H_5NH_3^+$). Because the $-NH_3^+$ group is strongly electron-withdrawing and meta-directing, a significant amount of the meta-product is formed, contrary to the typical ortho/para-directing nature of the $-NH_2$ group.

Step 2 (Step-by-Step Analysis of Product Distribution): [0.5 Mark]

• The reaction mixture contains both aniline and the anilinium ion.
• The $-NH_2$ group is ortho/para directing, while the $-NH_3^+$ group is meta-directing.
• Experimental data for the nitration of aniline in a strongly acidic medium yields the following distribution:
  • Para-nitroaniline: $51\%$
  • Meta-nitroaniline: $47\%$
  • Ortho-nitroaniline: $2\%$

Step 3 (Final Concluded Answer): [0.25 Mark]

Comparing the experimental percentages with the given options, the correct distribution is $51\%$ para, $47\%$ meta, and $2\%$ ortho.

Correct Option: (C)

💡 EL10 Concept Insight: Think of the amino group as a "door" that usually directs traffic to the sides (ortho/para). However, in acid, the group gets "locked" by a proton, which forces most of the traffic to the middle (meta) position, while the remaining "unlocked" molecules still send traffic to the sides.