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Question #44470

Difficulty: 8/10 | 🟢 Free

The Question

An equimolar mixture of (2E)-1-chloro-4-fluorobut-2-ene and (3E)-5-methoxypent-3-enenitrile is subjected to exhaustive ozonolysis followed by an oxidative workup using $\ce{H2O2}$ . The reaction yields four distinct substituted acetic acid derivatives: $\textbf{P}$ (chloro-substituted), $\textbf{Q}$ (fluoro-substituted), $\textbf{R}$ (methoxy-substituted), and $\textbf{S}$ (cyano-substituted). Which of the following represents the correct decreasing order of their acid dissociation constants ( $K_a$ ) in aqueous solution at 298 K?

Options

A.
$\textbf{S} > \textbf{Q} > \textbf{P} > \textbf{R}$
B.
$\textbf{Q} > \textbf{S} > \textbf{R} > \textbf{P}$
C.
$\textbf{Q} > \textbf{S} > \textbf{P} > \textbf{R}$
D.
$\textbf{S} > \textbf{Q} > \textbf{R} > \textbf{P}$

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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

Ozonolysis Fragmentation Patterns|Carboxylic Acid Strength|Hybridization and Geometry

Why This Question Is Tricky

Common Mistakes

This question tests the precise knowledge of the Inductive Effect ( $-I$ ) series and targets two major student misconceptions.

Trap 1: Students often assume Fluorine, being the most electronegative element, will exert the strongest $-I$ effect, incorrectly placing Fluoroacetic acid ( $\textbf{Q}$ ) above Cyanoacetic acid ( $\textbf{S}$ ).

They fail to account for the powerful electron-withdrawing nature of the $sp$ -hybridized carbon in the cyano group.

Trap 2: Students compare the electronegativity of Oxygen and Chlorine and incorrectly deduce that the methoxy group ( $\ce{-OCH3}$ ) has a stronger $-I$ effect than chlorine, placing $\textbf{R} > \textbf{P}$ .

They overlook that the alkyl group in $\ce{-OCH3}$ is electron-donating (+I), which significantly reduces the net inductive pull of the oxygen atom.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Hydrocarbons - Class 11 Part 2
Concept	Ozonolysis Fragmentation Patterns
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free