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Question #44440

Difficulty: 8/10 | 🟢 Free

The Question

Consider the hydration equilibria of the following carbonyl compounds in aqueous solution at 298 K to form their respective gem-diols: (I) \ce{CF3COCF3} (II) \ce{CF3CHO} (III) \ce{HCHO} (IV) \ce{CH3CHO} (V) \ce{CH3COCH3}

Let $K_I, K_{II}, K_{III}, K_{IV},$ and $K_V$ represent their respective hydration equilibrium constants. Which of the following sequences correctly represents the decreasing order of their $K_{eq}$ values?

Options

A.
$K_I > K_{II} > K_{III} > K_{IV} > K_V$
B.
$K_{III} > K_{II} > K_I > K_{IV} > K_V$
C.
$K_{II} > K_{III} > K_I > K_{IV} > K_V$
D.
$K_{III} > K_{IV} > K_{II} > K_V > K_I$

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

Hydrate Stability vs. Carbonyl|Nucleophilic Addition Sterics|Inductive Effect Trends

Why This Question Is Tricky

Common Mistakes

Students often memorize that 'formaldehyde forms the most stable hydrate due to lack of steric hindrance' and rigidly apply steric arguments to all nucleophilic additions.

This trap exposes the 'Chemical Exception' where profound electronic effects (strong $-I$ induction from \ce{-CF3} groups) completely override steric penalties.

The hidden variable is the thermodynamic destabilization of the highly electrophilic carbonyl ground state and the inductive stabilization of the gem-diol, which makes hexafluoroacetone's hydration overwhelmingly favorable despite its bulk.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Hydrate Stability vs. Carbonyl
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free