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Question #44271

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The Question

Element $\text{X}$ has its highest energy electrons in a subshell characterized by $(n+l) = 3$ and $l = 1$ . The subshell is exactly half-filled in its ground state. Compound $\text{A}$ is the simplest primary mono-nuclear aromatic amine containing element $\text{X}$ . Consider the following derivatives of $\text{A}$ in an aqueous medium at $298\text{ K}$ :

I. Compound $\text{A}$ II. $o$ -Methyl derivative of $\text{A}$ III. $m$ -Methyl derivative of $\text{A}$ IV. $p$ -Methyl derivative of $\text{A}$

Which of the following represents the correct decreasing order of basic strength ( $K_b$ ) of these compounds?

Options

A.
$\text{IV} > \text{III} > \text{I} > \text{II}$
B.
$\text{II} > \text{IV} > \text{III} > \text{I}$
C.
$\text{IV} > \text{II} > \text{III} > \text{I}$
D.
$\text{I} > \text{III} > \text{IV} > \text{II}$

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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

Energy of Subshells (n+l rule)|Aniline Resonance Pitfalls|Ortho-Effect in Anilines

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to bridge fundamental atomic structure (using the n+l rule to identify Nitrogen) with advanced organic reaction mechanisms.

The primary trap is the 'Ortho-Effect' in substituted anilines.

Students relying solely on linear electronic effects (+I, +H) will incorrectly predict o-toluidine to be highly basic due to the proximity of the electron-donating methyl group.

However, the hidden variable is the steric inhibition of solvation of the conjugate acid.

This steric hindrance overrides the electronic resonance/inductive effects, making o-toluidine the least basic of the series, completely flipping the expected thermodynamic stability order.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Structure of Atom - Class 11 Part 1
Concept	Energy of Subshells (n+l rule)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free