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Question #44570

Difficulty: 8/10 | 🟢 Free

The Question

A 3d transition metal $M$ exhibits an anomalously negative standard reduction potential $E^\circ(M^{2+}/M)$ compared to the general trend of the series, attributed to the exchange energy stabilization of its half-filled $d$ -subshell. Aniline is treated with an equimolar amount of anhydrous \ce{MCl2} in an inert solvent to form a coordination complex. This complex is then reacted with one equivalent of \ce{Br2} at 298 K. Following standard aqueous workup, the major organic product $P$ is isolated.

Given: $E^\circ(\ce{Br2/Br^-}) = +1.09$ V $E^\circ(\ce{Fe^{3+}/Fe^{2+}}) = +0.77$ V $E^\circ(\ce{Mn^{3+}/Mn^{2+}}) = +1.51$ V

Identify the major organic product $P$ .

Options

A.
4-bromoaniline
B.
3-bromoaniline
C.
2,4,6-tribromoaniline
D.
2-bromoaniline

Check Your Answer

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

E° (M²⁺/M) Anomalies|Electrophilic Substitution Control|Ortho-Effect in Anilines

Why This Question Is Tricky

Common Mistakes

The question tests the intersection of Periodic Trends ( $E^\circ$ anomalies), Redox Chemistry, and Electrophilic Aromatic Substitution.

Students often memorize that 'Lewis acids coordinate to aniline and direct meta' (e.g., \ce{AlCl3}).

The hidden variable here is the specific electronic configuration of \ce{Mn^{2+}} ( $d^5$ ).

Its stability prevents oxidation by \ce{Br2} (unlike \ce{Fe^{2+}}) and results in weak Lewis acidity.

This weak coordination creates a 'Goldilocks' scenario: it is weak enough to preserve the $+M$ activating effect of the \ce{-NH2} group, but bulky enough to sterically shield the ortho positions, overriding the standard electronic distribution and yielding the para product.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	D and F Block Elements - Class 12
Concept	E° (M²⁺/M) Anomalies
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free