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Question #44976

Difficulty: 8/10 | 🟢 Free

The Question

A non-reducing trisaccharide $X$ upon exhaustive methylation followed by strong acidic hydrolysis yields equimolar amounts of 2,3,4,6-tetra- $O$ -methyl-D-galactose, 2,3,4-tri- $O$ -methyl-D-glucose, and 1,3,4,6-tetra- $O$ -methyl-D-fructose.

One mole of $X$ is subjected to mild acidic hydrolysis ( $0.01\ M\ HCl$ , $20^\circ C$ ) which selectively cleaves the most kinetically labile glycosidic linkage to form a monosaccharide $Y$ and a disaccharide $Z$ . The resulting mixture is then treated with excess phenylhydrazine in an acetate buffer (pH 4.5) at $100^\circ C$ until osazone formation is complete.

Determine the total number of moles of phenylhydrazine consumed by the carbohydrate mixture per mole of $X$ .

Options

A.
6 moles
B.
3 moles
C.
9 moles
D.
0 moles

Check Your Answer

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

Osazone Formation Logic|Reducing Sugar Criteria|Glycosidic Linkage Geometry

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of structural carbohydrate chemistry and chemical kinetics.

The primary trap is 'Glycosidic Linkage Occlusion' and the differential stability of acetals.

Students often fail to recognize that furanosides are significantly more acid-labile than pyranosides.

A common error is assuming complete hydrolysis (yielding 9 moles of phenylhydrazine consumption) or incorrect cleavage of the pyranoside bond (yielding 3 moles, assuming sucrose is formed and remains non-reducing).

Furthermore, students must correctly apply the stoichiometry of Fischer's osazone formation, remembering that each reducing sugar unit (whether mono- or disaccharide) consumes exactly 3 moles of phenylhydrazine.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	Osazone Formation Logic
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free