EM 241 IRALITY AP 4 ASSIGN 1. Assume that a particular reaction gives the following two enantiomers as products in the following ratio. What is the enantiomeric excess (% ee) associated with this reaction? A. 15% B. 85%. 70% D. 80% E. 95% 2. Mevacor is used clinically to lower serum cholesterol levels. ow many chirality centers does Mevacor have? learly designate each chirality center on the figure. 3 3 3 3 Mevacor 3. ow many stereoisomers of mevacor are possible? 4. ommercial samples of (+)- -pinene typically give 92% of the maximum optical rotation possible for (+)- -pinene are said to be 92% optically pure. What proportions of the enantiomers are present? A. 92% (+) 8% (-) B. 92% (-) 8% (+). 84% (+) 16% (-) D. 96% (+) 4% (-) E. 88% (+) 12% (-) 5. Which of the following molecules is the enantiomer of (2S, 3S )-2-omo-3-chlorobutanoic acid? A B D E 6. ow many optical isomers of 1,2-dichlorocyclohexane are there? A. one B. two. three D. four 1 P a g e
7. Which of the following molecules contains three stereocenters? A B D E 8. The following Fischer projection corresponds to which stereochemistry? A B D E 9. Which of the following molecules is not chiral? A B D E 10. Which of the following molecules has a single stereocenter in the S configuration? A B D E 11. Which of the following molecules could exist as a total of three stereoisomers? A B D E 12. Assign an (R)-(S) stereochemistry to each of the following molecules. A. S, S, S B. R, S, S. S, R, S D. S, S, R E. S, R, R 2 P a g e
13. Which of the following pairs of molecules represents a pair of enantiomers? A. B.. D. E. 14. Indicate which of the following Fischer projections correctly represents (2R, 3R )-3-chloro-2-methoxypentane (shown below as a zigzag structure). A B D E 15. During the course of your career as a natural products chemist you isolate a new compound from a plant in South America that has excellent cytotoxic activity against tumor cells. Because you have isolated the compound as a pure enantiomer, you wish to report its optical activity. A 0.50-g sample of the compound is placed in 10 ml of ethanol in a sample tube placed in the polarimeter. The observed optical rotation (a) is measured to be +0.53 degrees. If the length of the sample tube (l ) is 10 cm, what is the calculated value for the specific rotation of this new compound? 16. Which of the following is not true for enantiomers? A. They have the same boiling point. B. They have the same melting point.. They have the same chemical reactivity with achiral reagents. D. They have the same chemical reactivity with chiral reagents. E. They have the same density. F. They have the same specific rotation. A. F B. D F. F D. all but F 17. Which is/are optically inactive? A. a racemic mixture B. a meso compound. every achiral compound D. a 50-50 mixture of R S enantiomers E. all of the above 3 P a g e
18. The correct stereochemical designation for the compound shown at the right is -3,4-hexanediol A. (3R, 4R) B. (3S, 4S). (3R, 4S) D. (3R) E. (4S) 2 3 2 3 19. Arrange the following three groups in the order of highest to lowest priority. -(=S)- 3 -(=)- 3 -(=)- 3 A B A. A > B > B. > B > A. A > > B D. B > > A 20. Which is/are optically inactive? (a) a racemic mixture (c) every achiral compound (e) all of the above (b) a meso compound (d) a 50:50 mixture of R S enantiomers 21. As the reaction shown proceeds, what happens to the optical activity of the solution? (a) increases (b) drops to zero (c) changes sign (d) stays the same (e) impossible to predict (R) 3 2 3 = 2 + 2 Ni 3 2 3 2 3 NAME DATE ANSWER SEET EM 241 AP 4 ASSIGN 1. 7. 13. 19. 2. 8. 14. 20. 3. 9. 15. 21. 4. 10. 16. 22. next page 5. 11. 17. 6. 12. 18. FALL 2018 4 P a g e
22. In the space provided, identify the relation between the structures in each of the following pairs: S if they are constitutional isomers D if they are diastereomers X if they are different compounds that are not isomers E if they are a pair of enantiomers I if they are two different representations of the same compound (not isomers) (a) 2 (g) l l (b) 2 3 (h) l 3 2 3 3 l (c) 2 3 (i) 3 l 3 2 3 3 2 2 3 l (d) 3 3 3 3 (j) l l (e) (k) l l l l (f) (l) l l l l 3 3 3 2 5 P a g e