CH 3 H C 2 H 5. C Cl C H. H 3 C Cl H H 5 C 2. H Cl. Cl H. C Cl H. H Cl. Problem Set 7: Stereochemistry-2

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1 Problem Set 7: Stereochemistry-2 hemistry 260 Organic hemistry 1. ow many constitutional isomers of 7 16 have stereogenic centres? (1) 1 (2) 2 (3) 3 (4) 4 (5) none 2. Indicate which of the following compounds are chiral (can exhibit optical activity). (a) 3-methylhexane (b) 3-ethylhexane (c) 3-chloro-1-butene (d) 3-methyl-1-butene 3. Name the following compound: 3 4. Which of the following pairs are enantiomers? (1) (2) (3) (4) Br Br O 3 1

2 5. Which of the following compounds is chiral (taking into consideration conformational interconversions)? (1) (2) (3) (4) O O 6-7. Assign the following pairs of molecules as: (1) enantiomers (2) diastereomers (3) constitutional isomers (4) identical molecules 6. O Octane and 3-ethyl-2-methylpentane are: (1) not isomers (2) enantiomers (3) diastereomers (4) constitutional isomers ow many total stereoisomers are possible with the following molecules? (1) one (2) two (3) three (4) four (5) six 9. 2,3-dihydroxypentane 10. 1,3-dichlorocyclopentane 11. methylcyclohexane 12. 2,5-dichlorohexane 2

3 13. In a study of chlorination of propane, four products (A, B,, and D) of formula were isolated. Each was chlorinated further, and the number of trichloro products ( ) obtained from each was determined. A gave one trichloro product, B gave two, and and D each gave three. By another synthetic method, compound was obtained in chiral (optically active) form. When chiral (optically active) was chlorinated, one of the trichloropropanes (E) obtained was optically active, and the other two were optically inactive. What are the structures and systematic names of A, B,, D, and E? 14. (R)-Epinephrine has a specific rotation of -51. A sample that contains a mixture of R- and S-isomers was found to have a rotation of What is the percentage of R and S isomers in this sample? 15. This is a modified version of question #8 from the Stereochemistry-1 problem set. Given the following five structures, indicate for each pair listed below whether the structures are identical, enantiomers or diastereomers. (a) A and B (b) A and E (c) B and E (d) and D (you should be able to answer this now) 3

4 16. ircle all the achiral compounds. 17. Provide a name for the following compound 18. Fluticasone propionate (marketed under the tradename Flovent TM ) is a steroid based drug that is used in many inhalers as a treatment during an asthma attack. (a) ow many chirality centres are located in Flovent? (b) Draw the enantiomer of Flovent 4

5 19. (-) Paroxetine, also known as Paxil (shown below) is a selective serotonin reuptake inhibitor that is used as an antidepressant. (-) Paroxetine has affinity for various protein receptors. (a) Draw the enantiomer of (-) Paroxetine. (b) Would you expect (-) Paroxetine and its enantiomer to have the same biological effect? (In other words, would (-) Paroxetine and its enantiomer have the same interaction with the same protein target?) Briefly justify your answer. (c) Would you expect (-) Paroxetine and its enantiomer to have the same boiling point? Briefly justify your answer. (d) (-) Paroxetine has a specific rotation of at 298K. What is the specific rotation of its enantiomer under the same conditions? (e) What would be the specific rotation of a sample that contains 39% of (-) Paroxetine and 61% of its enantiomer? 5

6 20. Ampicillin has been one of the most widely prescribed antibiotics. In the structure of ampicillin below, clearly circle all the carbon asymmetric centers. 21. Name the following compounds. Be sure to indicate stereochemistry where appropriate. 22. ircle all the chiral compounds 6

7 23. Draw the enantiomer of each of the following molecules. 7

8 24. Below are eight pairs of structural formulas. In the box to the right of each pair, place the number (from the six terms listed below) that BEST describes the relationship between the two structures. NOTE: Each term may be used more than once and not all terms need be used. ALSO, IRLE ALL TE MESO OMPOUNDS. 1. Identical 4. onstitutional Isomers 2. Diastereomeers 5. Enantiomers 3. onformers 6. None of the above 8

9 25. In the pharmaceutical business, a blockbuster drug is one which achieves sales up to and exceeding a billion dollars a year. opidogrel, marketed under the trade name Plavix TM, is a blockbuster drug that is a potent anti-clotting agent. Studies suggest that the compound below is the active compound; the opposite enantiomer has been shown to have no biological effect. (a) Assign the asymmetric centre as either R or S (b) Draw the biologically inactive enantiomer of opidogrel 9