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Question #44948
The Question
D-Glucose is treated with excess \ce{CH3OH} in the presence of dry \ce{HCl} gas to yield compound (a mixture of anomers). Compound is then subjected to the following reaction sequence:
- \ce{HCN (aq)}, trace \ce{KCN}
- Dilute \ce{H3O+},
- \ce{Br2 / H2O}
Identify the major final product(s) of this sequence.
Options
- A.
D-Gluconic acid
- B.
A mixture of D-glucoheptonic acid and D-mannoheptonic acid
- C.
Methyl D-gluconate
- D.
A mixture of D-glucoheptose and D-mannoheptose
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
D-Glucose Anomeric Equilibrium|Reducing Sugar Criteria|Kiliani-Fischer Chain Extension
Why This Question Is Tricky
Common Mistakes
This question tests the structural requirements for the reactions of reducing sugars.
Students often memorize the Kiliani-Fischer synthesis (chain extension via \ce{HCN}) without realizing it strictly requires a free carbonyl group.
By converting D-glucose to a methyl glycoside (an acetal), the anomeric center is blocked, preventing the formation of the open-chain aldehyde.
The trap is assuming the chain extension occurs anyway, leading to the incorrect 7-carbon heptonic acids.
The correct path requires identifying the inertness of the glycoside to \ce{HCN}, followed by its acid-catalyzed hydrolysis back to D-glucose, and subsequent mild oxidation to D-gluconic acid.
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 |