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Question #44950

Difficulty: 8/10 | 🟢 Free

The Question

Consider the reaction of the following four carbohydrate derivatives with an excess of phenylhydrazine ( $\ce{PhNHNH2}$ ) in an acetate buffer (pH $\approx 4.5$ ) at $100^\circ\text{C}$ :

(I) D-Glucose (II) D-Fructose (III) 2-Deoxy-D-glucose (IV) Methyl $\alpha$ -D-glucopyranoside

Let $n_1, n_2, n_3,$ and $n_4$ be the number of equivalents of $\ce{PhNHNH2}$ consumed per mole of I, II, III, and IV respectively, to form their final stable nitrogen-containing products $P_1, P_2, P_3,$ and $P_4$ . Which of the following options correctly lists the values of $n_1, n_2, n_3, n_4$ and the correct structural relationship between the products?

Options

A.
$n_1 = 3, n_2 = 3, n_3 = 1, n_4 = 0$ ; $P_1$ and $P_2$ are identical
B.
$n_1 = 2, n_2 = 3, n_3 = 1, n_4 = 0$ ; $P_1$ and $P_2$ are diastereomers
C.
$n_1 = 3, n_2 = 3, n_3 = 2, n_4 = 1$ ; $P_1$ and $P_2$ are identical
D.
$n_1 = 3, n_2 = 2, n_3 = 1, n_4 = 0$ ; $P_1$ and $P_2$ are structural isomers

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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

D-Glucose Anomeric Equilibrium|Osazone Formation Logic|Tollens vs. Fehling Specificity

Why This Question Is Tricky

Common Mistakes

The question tests the mechanistic boundaries of osazone formation and the anomeric equilibrium.

The primary trap is the misconception that osazone formation consumes only 2 equivalents of phenylhydrazine, ignoring the crucial redox equivalent.

Furthermore, it introduces a 'hidden variable' via 2-deoxy-D-glucose, testing the student's knowledge that the C2 hydroxyl group is mechanistically mandatory for the Amadori-type tautomerization and subsequent oxidation.

Finally, it evaluates the distinction between hemiacetals (which equilibrate to reactive open-chain forms) and acetals (which are kinetically locked under mild pH 4.5 conditions).

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	D-Glucose Anomeric Equilibrium
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free