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Question #44647

Difficulty: 8/10 | 🟢 Free

The Question

A student attempts to synthesize a Grignard reagent by reacting 1-bromo-4-chlorobenzene with $1.0$ equivalent of Magnesium turnings in THF. Unknown to the student, the THF solvent is contaminated with exactly $1.0$ equivalent of $\ce{D2O}$ , resulting in the formation of organic compound $\textbf{P}$ . Compound $\textbf{P}$ is subsequently subjected to nitration using a mixture of concentrated $\ce{HNO3}$ and $\ce{H2SO4}$ at $298\text{ K}$ to form the major organic product $\textbf{Q}$ . Identify $\textbf{Q}$ .

Options

A.
1-chloro-4-nitrobenzene
B.
1-chloro-4-deutero-2-nitrobenzene
C.
1-bromo-4-deutero-2-nitrobenzene
D.
1-chloro-4-deutero-3-nitrobenzene

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Aryl Halide Resonance|Grignard Reaction Pathways|Grignard Reagent Sensitivity

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to integrate thermodynamic bond strengths (C-Br vs C-Cl), the extreme kinetic sensitivity of Grignard reagents to protic solvents (D2O quenching), and the nuances of Electrophilic Aromatic Substitution (EAS).

The core trap is the 'Hidden Variable' of the Kinetic Isotope Effect (KIE): students often assume the introduced Deuterium label is permanent and will force ortho-substitution to preserve the C-D bond.

However, since C-H/C-D cleavage is not the rate-determining step in nitration, the reaction proceeds normally at the sterically favored para position, resulting in the unexpected loss of the D-label.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Haloalkanes and Haloarenes - Class 12
Concept	Aryl Halide Resonance
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free