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Question #45089

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The Question

An amount of $24.6\text{ g}$ of nitrobenzene ( $\ce{C6H5NO2}$ ) is treated with an excess of $\ce{LiAlH4}$ in anhydrous diethyl ether at $298\text{ K}$ . The reaction goes to completion, yielding a major organic product $\textbf{Y}$ . Subsequently, $\textbf{Y}$ is subjected to complete reductive cleavage using $\ce{SnCl2}$ in aqueous $\ce{HCl}$ , followed by neutralization with excess $\ce{NaOH}$ , to yield a single organic compound $\textbf{Z}$ . Which of the following correctly represents the theoretical yield of $\textbf{Y}$ (in grams) and the number of moles of $\ce{Br2}$ required for the complete bromination of one mole of $\textbf{Z}$ in an aqueous medium? (Given molar masses in g/mol: $\ce{C}=12$ , $\ce{H}=1$ , $\ce{N}=14$ , $\ce{O}=16$ )

Options

A.
Yield of $\textbf{Y} = 18.2\text{ g}$ ; Moles of $\ce{Br2} = 3$
B.
Yield of $\textbf{Y} = 18.6\text{ g}$ ; Moles of $\ce{Br2} = 3$
C.
Yield of $\textbf{Y} = 36.4\text{ g}$ ; Moles of $\ce{Br2} = 3$
D.
Yield of $\textbf{Y} = 18.2\text{ g}$ ; Moles of $\ce{Br2} = 6$

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Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Reaction Intermediates Stability|Reduction Selectivity (Sn/HCl vs LiAlH4)|Reaction Progress Coordinate

Why This Question Is Tricky

Common Mistakes

This problem tests a critical exception in reduction selectivity and stoichiometric accounting.

Students often rote-learn that $\ce{LiAlH4}$ reduces $\ce{-NO2}$ to $\ce{-NH2}$ .

However, for aryl nitro compounds in anhydrous media, the reduction halts at the azo stage (azobenzene) due to a bimolecular pathway.

Failing to account for this intermediate alters the stoichiometric equivalence, halving the expected molar yield (Trap B assumes aniline is formed directly; Trap C forgets the stoichiometric coefficient division).

Furthermore, it tests the knowledge of reductive cleavage of azo bonds and the subsequent electrophilic aromatic substitution of the resulting aniline, ensuring students read carefully to calculate bromination per mole of $\textbf{Z}$ , not $\textbf{Y}$ (Trap D).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Organic Chemistry – Some Basic Principles and Techniques - Class 11 Part 2
Concept	Reaction Intermediates Stability
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free