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Question #44975
The Question
An equimolar mixture containing each of D-glucose, D-mannose, D-fructose, D-galactose, D-talose, D-ribose, and sucrose is heated with an excess of phenylhydrazine in an aqueous acetate buffer (pH ) at until all possible reactions (including the complete hydrolysis of any susceptible glycosidic bonds) have gone to completion.
Let be the number of structurally distinct osazones formed in the final mixture. Let be the total number of moles of phenylhydrazine consumed. Let be the total number of moles of aniline produced as a byproduct.
Calculate the value of .
Options
- A.
35
- B.
27
- C.
38
- D.
30
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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
Osazone Formation Logic|Epimerization vs Anomerization
Why This Question Is Tricky
Common Mistakes
The problem tests three critical concepts in carbohydrate chemistry.
First, the 'Osazone Epimerization Trap': students must recognize that osazone formation destroys the C-2 stereocenter, meaning C-2 epimers (e.g., D-glucose/D-mannose and D-galactose/D-talose) and their corresponding ketoses (D-fructose) yield identical osazones.
Second, the stoichiometry of the reaction: exactly 3 equivalents of phenylhydrazine are consumed per mole of sugar, with one equivalent acting as an oxidizing agent to produce exactly 1 mole of aniline.
Finally, the 'Hidden Reaction': failing to account for the acid-catalyzed hydrolysis of the non-reducing sugar sucrose into D-glucose and D-fructose under the reaction conditions leads to a significant stoichiometric error.
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 |