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Question #44444

Difficulty: 8/10 | 🟢 Free

The Question

D-Glucose undergoes mutarotation in aqueous solution at 298 K298 \text{ K} via an open-chain intermediate. The overall process involves the α\alpha-pyranose (AA), β\beta-pyranose (BB), the open-chain free aldehyde (II), and its gem-diol hydrate (HH). The mutarotation mechanism is strictly mediated by the free aldehyde (II):

\ceA<=>[k1][k−1]I<=>[k2][k−2]B\ce{A <=>[k_1][k_{-1}] I <=>[k_2][k_{-2}] B}

The free aldehyde is in rapid equilibrium with its hydrate:

\ceI+H2O(l)<=>[Kh]H\ce{I + H2O(l) <=>[K_h] H}

where the hydration equilibrium constant is Kh=[H][I]=3.0K_h = \frac{[H]}{[I]} = 3.0. At equilibrium, the mole fractions of the cyclic species relative to the total dissolved glucose are [A]=0.36[A] = 0.36 and [B]=0.64[B] = 0.64. The total mole fraction of the open-chain species (I+HI + H) is experimentally determined to be 2.0×10−42.0 \times 10^{-4}.

Given that the rate constant for the ring closure of the α\alpha-anomer is k−1=14.4 s−1k_{-1} = 14.4 \text{ s}^{-1}, determine the rate constant for the ring opening of the α\alpha-anomer (k1k_1).

Options

  • A.

    2.0×10−3 s−12.0 \times 10^{-3} \text{ s}^{-1}

  • B.

    8.0×10−3 s−18.0 \times 10^{-3} \text{ s}^{-1}

  • C.

    6.0×10−3 s−16.0 \times 10^{-3} \text{ s}^{-1}

  • D.

    1.1×10−3 s−11.1 \times 10^{-3} \text{ s}^{-1}

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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 [I]=2.0×10−4[I] = 2.0 \times 10^{-4}, leading directly to the incorrect answer of 8.0×10−3 s−18.0 \times 10^{-3} \text{ s}^{-1}.

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

SubjectChemistry
ChapterAldehydes, Ketones, and Carboxylic Acids - Class 12
ConceptHydrate Stability vs. Carbonyl
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree