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Question #44045

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The Question

An unknown amine $\mathbf{X}$ with the molecular formula \ce{C4H11N} is subjected to a series of qualitative tests. I. $\mathbf{X}$ reacts with \ce{CHCl3} and ethanolic \ce{KOH} at $343 \text{ K}$ to produce a highly offensive-smelling compound $\mathbf{Y}$ . II. $\mathbf{X}$ reacts with benzenesulfonyl chloride (\ce{PhSO2Cl}) to form a crystalline solid $\mathbf{Z}$ . III. Surprisingly, solid $\mathbf{Z}$ is found to be completely insoluble in $10\% \text{ NaOH(aq)}$ at $298 \text{ K}$ , despite $\mathbf{X}$ passing test I. Which of the following correctly identifies $\mathbf{X}$ and the primary chemical reason for the anomalous behavior in Test III?

Options

A.
$\mathbf{X}$ is 2-methylpropan-2-amine; $\mathbf{Z}$ is insoluble because the massive steric bulk of the \textit{tert}-butyl group shields the $N-H$ proton and prevents the solvation of the sulfonamide anion.
B.
$\mathbf{X}$ is $N$ -ethylethanamine; $\mathbf{Z}$ is insoluble because secondary amines form $N,N$ -dialkylsulfonamides which lack an acidic proton.
C.
$\mathbf{X}$ is butan-1-amine; $\mathbf{Z}$ is insoluble because the hydrophobic nature of the linear alkyl chain overcomes the hydration energy of the sodium salt.
D.
$\mathbf{X}$ is 2-methylpropan-1-amine; $\mathbf{Z}$ is insoluble because the strong $+I$ effect of the isobutyl group severely decreases the acidity of the $N-H$ proton.

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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

Carbylamine Reaction Specificity|Hinsberg Reagent Selectivity|Inductive Effect Trends

Why This Question Is Tricky

Common Mistakes

The problem tests a critical exception in the Hinsberg test for amine classification.

Students are taught that primary amines form sulfonamides soluble in aqueous NaOH, while secondary amines form insoluble sulfonamides.

The trap exploits 2-methylpropan-2-amine (tert-butylamine), a primary amine that gives a positive Carbylamine test but fails the Hinsberg solubility test.

The bulky tert-butyl group sterically shields the acidic N-H proton and severely hinders the solvation of the resulting anion, rendering N-tert-butylbenzenesulfonamide insoluble in 10% NaOH.

This forces students to reconcile conflicting qualitative data using steric and solvation principles rather than blindly applying the standard primary/secondary amine heuristic.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Amines - Class 12
Concept	Carbylamine Reaction Specificity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free