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Question #44184

Difficulty: 8/10 | 🟢 Free

The Question

Consider the following substituted amines in an aqueous solution at $298\text{ K}$ : (I) Aniline (II) $2,6$ -Dimethylaniline (III) $N,N$ -Dimethylaniline (IV) $N,N,2,6$ -Tetramethylaniline

Identify the correct decreasing order of their basic strength ( $K_b$ ).

Options

A.
IV > III > I > II
B.
III > I > II > IV
C.
II > I > III > IV
D.
IV > II > III > I

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

Resonance Stability Criteria|Aniline Resonance Pitfalls|Inductive Effect Trends

Why This Question Is Tricky

Common Mistakes

This problem tests the critical boundary between the 'Ortho Effect' and 'Steric Inhibition of Resonance' (SIR).

Students typically learn that steric hindrance near the basic site decreases basicity in aqueous media due to poor solvation of the conjugate acid (which correctly explains why 2,6-dimethylaniline is weaker than aniline).

The trap lies in applying this logic to N,N,2,6-tetramethylaniline.

Here, the hidden variable is the conformational change: the extreme steric clash forces the dimethylamino group out of the ring's plane.

This shuts down resonance delocalization (SIR), localizing the lone pair on nitrogen and causing a massive spike in basicity that completely eclipses the loss of solvation energy.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Bonding and Molecular Structure - Class 11 Part 1
Concept	Resonance Stability Criteria
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free