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Question 1 of 5
1. Question
If the specific rotation of (S)-aspartic acid is +24.5, what is the specific rotation of (R)-aspartic acid?
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Question 2 of 5
2. Question
A solution of enantiomerically pure (S)-2-methyl-1,2-butanediol, shown below, was prepared by dissolving 0.800 g in 10.0 mL of ethanol. The solution was added to a 10.0 cm sample cell and the optical activity was determined to be −0.74. What is the specific rotation of (R)-2-methyl-1,2-butanediol?
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Question 3 of 5
3. Question
A mixture of enantiomers of a newly-developed drug candidate is composed of 64.0% of the dextrorotatory isomer and 36.0% of the levorotatory isomer. What is the percent enantiomeric excess of this mixture?
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Question 4 of 5
4. Question
You find a vial labeled only as “epinephrine enantiomers”. You measure the optical activity of the sample and find it has an observed rotation of +22.3°. What is the percent enantiomeric excess (% ee) of the sample? Biologically-active epinephrine, shown below has a specific rotation of −50.0.
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The % ee is %. Enter your answer to one decimal place.
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Question 5 of 5
5. Question
CHALLENGE
The two cyclic forms of glucose are α-D-glucopyranose and β-D-glucopyranose. In solutions of glucose, these two forms exist in equilibrium. The specific rotation of α-D-glucopyranose is +112, while that of β-D-glucopyranose is +18.7. If the specific rotation of an equilibrium mixture of these two diastereomers is +52.7, what percent of the mixture exists as β-D-glucopyranose?
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Enter your answer to the nearest percent. %
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As noted in the question, and as evidenced by their specific rotations, α-D-glucopyranose and β-D-glucopyranose are diastereomers, not enantiomers. Therefore, each will contribute to the optical activity of the mixture in proportion to the amount present. A system of equations will have to be setup, one equation that relates the fraction of each present in the sample to the specific rotation of the mixture, and another that relates the fractions themselves to the whole (the fraction of each must add to 1.0).
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