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Question #43998

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The Question

Consider the following carbohydrate derivatives: \begin{itemize} \item \textbf{X}: 1-O-acetyl- $\beta$ -D-glucopyranose \item \textbf{Y}: Methyl $\beta$ -D-glucopyranoside \item \textbf{Z}: 2-O-methyl-D-glucose \end{itemize} Each compound is independently heated with an excess of phenylhydrazine in an aqueous acetate buffer (pH $\approx 4.5$ ) at $100^\circ\text{C}$ . Which of the following correctly describes the major outcome for each compound?

Options

A.
\textbf{X} yields D-glucosazone; \textbf{Y} remains unreacted; \textbf{Z} yields a monophenylhydrazone.
B.
\textbf{X} and \textbf{Y} remain unreacted; \textbf{Z} yields D-glucosazone.
C.
\textbf{X} yields a monophenylhydrazone; \textbf{Y} yields D-glucosazone; \textbf{Z} remains unreacted.
D.
All three compounds yield D-glucosazone due to the acidic hydrolysis of their respective protecting groups.

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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

Esterification Reversibility|Reducing Sugar Criteria|Osazone Formation Logic

Why This Question Is Tricky

Common Mistakes

The question tests the dynamic nature of 'reducing sugar' criteria and the mechanistic requirements for osazone formation.

The primary trap is assuming that 1-O-acetyl-beta-D-glucopyranose (X) is permanently non-reducing because its anomeric center is protected.

Students overlook that anomeric esters are susceptible to nucleophilic acyl substitution (aminolysis) by phenylhydrazine, which unmasks the free sugar in situ.

A secondary trap is assuming that 2-O-methyl-D-glucose (Z) can form an osazone, failing to recognize that the C2 hydroxyl must be free for the Amadori-type rearrangement to proceed.

Finally, distinguishing the stability of an ester (X) versus an acetal (Y) under mildly acidic/nucleophilic conditions is a classic test of functional group reactivity.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Aldehydes, Ketones, and Carboxylic Acids - Class 12
Concept	Esterification Reversibility
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free