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Question #44913

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The Question

Aniline is treated with a nitrating mixture (conc. \ce{HNO3} and conc. \ce{H2SO4}) at 288 K, yielding three mononitrated products $X$ , $Y$ , and $Z$ with approximate yields of $51\%$ , $47\%$ , and $2\%$ respectively. Product $Y$ is isolated and subjected to the following sequence of reactions:

\ce{NaNO2 / HCl}, 273 K
\ce{HBF4}, followed by $\Delta$
\ce{Sn / HCl}, followed by \ce{NaOH (aq)}
Excess \ce{Br2 (aq)}

Identify the final product formed and the key species whose formation dictates the $47\%$ yield of $Y$ in the initial nitration step.

Options

A.
2,4,6-Tribromo-3-fluoroaniline ; Anilinium ion
B.
4,6-Dibromo-2-fluoroaniline ; Anilinium ion
C.
2,6-Dibromo-4-fluoroaniline ; Unprotonated aniline
D.
2,4,6-Tribromo-3-fluoroaniline ; Unprotonated aniline

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Electrophilic Substitution Control|Aniline Resonance Pitfalls|Ortho-Effect in Anilines

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Aniline Resonance Pitfall' under strongly acidic conditions.

Students often assume the strongly activating \ce{-NH2} group will exclusively direct ortho/para.

However, the hidden variable is the reaction medium: concentrated \ce{H2SO4}/\ce{HNO3} protonates aniline to the anilinium ion (\ce{-NH3+}), which lacks a lone pair for resonance (+M effect) and exerts a strong -I effect, making it meta-directing.

The trap forces students to correctly assign the 47% yield to the meta-isomer, track it through a diazonium displacement and reduction, and finally predict the regiochemistry of exhaustive bromination where the \ce{-NH2} group dominates the directing effects over the halogen.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Amines - Class 12
Concept	Electrophilic Substitution Control
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free