Before You Begin
Question #44951
The Question
D-Glucose exists in a catalytic solvent system at as an equilibrium mixture of - and -anomers. The standard free energy change for the mutarotation equilibrium () is .
Excess acetic anhydride is added to completely acetylate the glucose. Under these specific conditions, the rate of mutarotation is significantly faster than the rate of esterification, placing the reaction under Curtin-Hammett control.
The absolute free energy of the transition state () for the rate-determining step of the -anomer acetylation is lower than that of the -anomer acetylation.
Calculate the mole percentage of -D-glucopyranose pentaacetate in the final product mixture.
(Given: at , , )
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Numerical_Precision
Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.
Concepts Behind This Question
D-Glucose Anomeric Equilibrium|Esterification Reversibility|Nucleophilic Acyl Substitution
Why This Question Is Tricky
Common Mistakes
This question tests the Curtin-Hammett principle.
A common trap is assuming the major product derives from the major equilibrium isomer, or incorrectly calculating the product ratio by multiplying the equilibrium constant by the ratio of activation energies while confusing absolute transition state energy () with activation energy ().
The ground state equilibrium constant () is a distractor; under Curtin-Hammett conditions, the product ratio is determined entirely by the absolute free energy difference of the transition states.
Students who mistakenly use the value as the difference in activation energies () will incorrectly calculate a product ratio of 3:1, leading to the 75.0% distractor.
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 |