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Question #44444
The Question
D-Glucose undergoes mutarotation in aqueous solution at via an open-chain intermediate. The overall process involves the -pyranose (), -pyranose (), the open-chain free aldehyde (), and its gem-diol hydrate (). The mutarotation mechanism is strictly mediated by the free aldehyde ():
The free aldehyde is in rapid equilibrium with its hydrate:
where the hydration equilibrium constant is . At equilibrium, the mole fractions of the cyclic species relative to the total dissolved glucose are and . The total mole fraction of the open-chain species () is experimentally determined to be .
Given that the rate constant for the ring closure of the -anomer is , determine the rate constant for the ring opening of the -anomer ().
Options
- A.
- B.
- C.
- D.
Check Your Answer
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
Hydrate Stability vs. Carbonyl|D-Glucose Anomeric Equilibrium
Why This Question Is Tricky
Common Mistakes
This question tests the student's ability to distinguish between a reactive intermediate and a thermodynamic sink in a complex equilibrium.
The 'Hidden Variable' is the hydrate stability of the open-chain form.
Students often treat D-glucose as a simple hemiacetal and assume the entire measured 'open-chain' fraction is the reactive free aldehyde (ignoring the hydrate analogy).
If they fall for this trap, they will use , leading directly to the incorrect answer of .
Recognizing that the carbonyl form is a transient, low-concentration species in equilibrium with its hydrate is crucial for determining the true kinetic parameters of mutarotation.
Quick Facts About This Question
Question Information
| Subject | Chemistry |
| Chapter | Aldehydes, Ketones, and Carboxylic Acids - Class 12 |
| Concept | Hydrate Stability vs. Carbonyl |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |