Name __________________ Lab Section: Circle one. Chem 226 / Fall 2009 MW or TTh(11:00) or TTh(2:00) Answer questions #1-#30 on the Scantron. #1-20, 4pts each; #21-30, 2pts each; answer remaining questions on the exam [pt. values indicated]; [Exam = 130 possible raw pts total] 1. Catalytic hydrogenation of 100. mmol of a hydrocarbon with a molecular formula of C 16 H 24 consumed 800. mg of hydrogen. The molecule has: A) 0 pi bonds, 3 double bonds, and 1 ring B) 3 pi bonds, 3 double bonds, and 2 rings C) 4 pi bonds, 4 double bonds, and 1 ring D) 0 pi bonds, 4 double bonds, and 1 ring E) 0 pi bonds, 5 double bonds, and 0 rings 2. Which compound can have four stereoisomers? A) 5-bromo-2,4-dimethyl pentene B) 5-bromo-3,4-dimethyl-2-pentene C) 1-bromo-2,4-dimethyl-2-pentene D) 2-bromo-3,4-dimethyl pentene 3. Which of the following expressions is the experimentally observed rate law for an E2 reaction of an alkyl halide? A. rate = k[RX] B. rate = k[RX][base] C. rate = k[RX] 2 D. rate = k[base] 4. The most stable chair conformation of cis-1-tert-butyl-2-methylcyclohexane has A. both groups equatorial. B. both groups axial. C. the tert-butyl group equatorial and the methyl group axial. D. the tert-butyl group axial and the methyl group equatorial. 5. In the dehydrohalogenation of 2-bromobutane, which conformation below leads directly to the formation of cis- 2-butene? A. only I B. only II C. only III D. I and II
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Name __________________ Lab Section: Circle one. Chem 226 / Fall 2009 MW or TTh(11:00) or TTh(2:00) Answer questions #1-#30 on the Scantron. #1-20, 4pts each; #21-30, 2pts each; answer remaining questions on the exam [pt. values indicated]; [Exam = 130 possible raw pts total] 1. Catalytic hydrogenation of 100. mmol of a hydrocarbon with a molecular formula of C16H24 consumed 800. mg
of hydrogen. The molecule has:
A) 0 pi bonds, 3 double bonds, and 1 ring B) 3 pi bonds, 3 double bonds, and 2 rings C) 4 pi bonds, 4 double bonds, and 1 ring D) 0 pi bonds, 4 double bonds, and 1 ring E) 0 pi bonds, 5 double bonds, and 0 rings
2. Which compound can have four stereoisomers?
A) 5-bromo-2,4-dimethyl pentene B) 5-bromo-3,4-dimethyl-2-pentene C) 1-bromo-2,4-dimethyl-2-pentene D) 2-bromo-3,4-dimethyl pentene
3. Which of the following expressions is the experimentally observed rate law for an E2 reaction of an alkyl
halide?
A. rate = k[RX] B. rate = k[RX][base] C. rate = k[RX]2 D. rate = k[base]
4. The most stable chair conformation of cis-1-tert-butyl-2-methylcyclohexane has
A. both groups equatorial. B. both groups axial. C. the tert-butyl group equatorial and the methyl group axial. D. the tert-butyl group axial and the methyl group equatorial.
5. In the dehydrohalogenation of 2-bromobutane, which conformation below leads directly to the formation of cis-
2-butene?
A. only I B. only II C. only III D. I and II
6. Which of the following cannot undergo an E2 reaction?
A. only I B. only II C. only III D. I and III
7. Which of the following does not give 1,2-dimethylcyclohexene as one of the acid-catalyzed dehydration
products?
8. What is the slow, rate-determining step, in the acid-catalyzed dehydration of 2-methyl-2-propanol?
A. Protonation of the alcohol to form an oxonium ion. B. Loss of water from the oxonium ion to form a carbocation. C. Loss of a β-hydrogen from the carbocation to form an alkene. D. The simultaneous loss of a β-hydrogen and water from the oxonium ion.
9. Consider the potential energy diagram shown below for the acid catalyzed hydration of (E)-4-methyl-2-
pentene. Which of the following statements best describe the reaction?
A) B and D are Transition States; A and C are Intermediates; the rate determining step is the formation of A, which is less stable than C.
B) B and D are Transition States; A and C are Intermediates; the rate determining step is the formation of B, which is less stable than D.
C) A and C are Transition States; B and D are Intermediates; the rate determining step is the formation of D, which is more stable than B.
D) A and C are Transition States; B and D are Intermediates; the rate determining step is the formation of B, which is less stable than D.
10. Which of the following molecules are chiral?
A. only II B. only III C. II and III D. I, II, and III
11. Which one of the following reactions is not stereospecific? A) reaction of cis-2-butene with peroxyacetic acid B) hydroboration-oxidation of 1-methylcyclopentene C) addition of Br2 to trans-2-pentene D) addition of HBr to cis-2-butene in the presence of peroxides 12. Which best describes the product that is formed from the epoxidation of trans-3-hexene:
A) A single enantiomer B)A product with one chiral carbon atom C)An optically inactive meso form D) A racemic mixture
13. Which one of the following outlines the best synthesis of trans-2-chlorocyclohexanol? A) Heat a mixture of cyclohexanol and Cl2 to 400oC. B) 1. Treat cyclohexene with HCl; 2. Treat product of reaction 1 with peroxyacetic acid. C) 1. Hydrogenation of cyclohexene in the presence of Pt; 2. Treat product of reaction 1 with Cl2 in H2O. D) 1. Treat bromocyclohexane with KOC(CH3)3 in DMSO; 2. Treat product of reaction 1 with Cl2 in water. 14. A pure sample of an amino acid (+)-(S)-phenylalanine, which has a specific rotation of +70°, is reacted with a
racemic mixture of the analgesic ibuprofen to produce two diastereomeric amides, (+, +) and (+, -). The (+, -) diastereomer has a specific rotation of +7.0°. What are the percentages of the S- and R- enantiomers of ibuprofen contained in the (+, -) product?
A. 95% S, 5% R B. 90% S, 10% R C. 55% S, 45% R D. 52.5% S, 47.5% R E. Cannot determine
15. Which of the following Fischer projections corresponds to the compound shown below?
16. The four isomeric dimethylcyclopropanes are shown below. Identify two of the isomers which are related as diastereomers.
A. I and III B. I and IV C. II and III D. III and IV
17. Compound X, C5H10O, is optically active. The compound consumes one equivalent of hydrogen to give C5H12O.
The hydrogenation product is also optically active. Which compound below matches the information?
O
H
O
H
O
H
O
H
A) B)
C) D)
18. It is being debated whether or not ozone exists in humans as one of several different reactive oxygen species. In
a laboratory experiment, cholesterol, which is shown below, was treated with ozone followed by zinc in water. What is (are) the expected product(s)?
A) two different compounds with different respective functions: one an aldehyde and one a ketone B) two different compounds with the same function: a ketone C) a single compound with two new functions: an aldehyde and a ketone D) a single compound with two new functions: two different aldehydes E) a single compound with two new functions: two different ketones
19. Which of the following carbocations is (are) likely to undergo a rearrangement?
+
++
I II III
A. only I B. I and III C. II and III D. I, II, and III
20. Free radical polymerization of vinyl chloride CH2=CHCl plus vinylidene chloride CH2=CCl2 was studied by
the producers of Saran plastic wrap. Identify the polymer’s configuration which follows.
Cl
Cl
H
Cl
H
Cl
Cl
Cl
H
Cl
H
Cl
Cl
Cl
Cl
Cl
H
Cl
Cl
Cl
A. atactic B. syndiotactic C. isotactic D. stereotactic
True (A)/ False (B): Answer on Scantron If a molecule has a plane or center of symmetry it must be achiral. 21. If a molecule has only one stereogenic center it must be chiral. 22. The stereoisomer on the right is erythro in configuration, which is the mirror image of threo.
CHO
CH2OH
OHH
HHO
CH2OH
CHO
OHH
OHH
23. The following two structures are diastereomers.
H
H
Br
Br
Br
Br
24. Optically active starting materials will always produce optically active products.
An optically active (+)-(R)-alcohol isomerizes in acid to produce a mixture which has [∝]20 = 0°. 25. This is because all of the starting alcohol has been converted to the opposite enantiomer. 26. Bimolecular reactions have at 2 Transition States. 27. Carbon free radicals are trigonal pyramidal in shape. 28. The following free radical is formed in the propagation step when 1-hexene is treated with HBr and peroxides.
End of Multiple Choice
C
4
H
9
C
H
C
H
2
B
r
.
29. Halohydrins are produced from the regioselective, stereospecific addition of a halogen atom and water to a
carbon-carbon double bond. 30. The following Fisher structures are enantiomers.
31. [4pts] Only the (S)-enantiomer of the analgesic, ibuprofen is biologically active. Complete the perspective
drawing for the active isomer and its Fisher drawing next to it. Using the Cahn-Ingold-Prelog priority system, number the substituent groups in the Fisher drawing: 1, 2, 3, 4; where 1 = highest and 4 = lowest priority.
C
32. [4pts] The following thermodynamic data were obtained for experimental catalytic hydrogenation of 4 different
hydrocarbons with the same molecular formula. Match the structures to the data.
Compound Heat of Hydrogenation (kJ/mol) A) -186 B) -164 C) -162 D) 0
____ cyclopentane ____ (Z)-2-pentene
____ 2-methyl-2-butene ____ (E)-2-pentene
33. [6pts] Complete the mechanism for the following reaction. Draw structures for the three intermediates. Use
arrows for the electron movement to show each step in the formation of the alcohol. Use water in the last step.
H
+
/
H
2
O
H
+
O
H
2
C
H
3
C
H
3
C
H
3
O
H
C
H
3
End of True/ False
34. A. [5pts] Retrosynthesis: Consider the product alcohol III. Choose synthetic precursors: one from the three choices in column II and one from the 3 choices in column I. Circle your choices. Then select reagent(s) for the respective reactions to produce III from the reagents A-L. Draw arrows from the selected precursors to product and place the corresponding reagent letter above them.
I II
III
OH
Br
OH
ClBr
OH
I II
III
OH
Br
OH
ClBr
OH
B. [5pts] Provide line structures for the products of the following reactions with the reagents noted above. Circle any chiral carbons in the products. Complete the Fisher drawing for the reaction with E.
I
E
H
G
+ mirrorimage
I II
III
35. [6pts] Peramivir is a newly registered antiviral drug. The active stereoisomer and the IUPAC name are shown
below. It was approved on October 23rd for treatment of H1N1 influenza by the U.S. Food and Drug Administration. It was developed by BioCryst Pharmaceuticals in collaboration with Green Cross Pharmaceuticals in South Korea and with Shionogi Pharmaceuticals in Japan.
/
Peramivir is a neuraminidase inhibitor, acting as a competitive transition-state inhibitor of influenza neuraminidase and thereby preventing new viruses from emerging from infected cells. It is administered by injection and offers improved treatment over other antivirals, Tamiflu and Relenza that are presently in use. How many stereocenters are present in peramivir? __________ How many stereoisomers are possible? __________ Identify two different functions in the molecule. (Name them below and circle them in the structure above.) ____________________ ____________________ What is the absolute configuration of the carbon to the left of the * in the structure? ___________ A stereospecific synthesis of peramivir, BCX-1812, (RWJ-270201), has been reported by synthetic chemists affiliated with Green Cross/Shionogi, who have friends and associates currently studying Chem 226 topics. The synthesis reported an overall yield of 60% and an optical yield of 80% of the biologically active isomer. What is the relative configuration of the biologically active stereoisomer? (circle one): d- or l- What is the enantiomeric excess of the main stereoisomer of peramivir in the synthesized sample? ________ Which stereoisomer is in excess? (circle one): d- or l- What is the % of the biologically active stereoisomer present in the sample? _________
(+)(1S,2S,3S,4R)-3-[(1S)-1-acetamido-2-ethyl-butyl]-4-(diaminomethylideneamino)-2-hydroxy-cyclopentane-1-carboxylic acid; [∝]20 = +57°, c = 0.5, ethanol
*
A stereospecific synthesis of BCX-1812(RWJ-270201) has been reported : Ring opening of (-)-2-azabicyclo[2.2.1]hept-5-en-3-one (I) with methanolic HCl gives the methyl ester (II), which is N-protected with Boc2O and TEA yielding the carbamate (III). Cyclization of (III) with 2-ethyl-1-nitrobutane (IV) by means of phenyl isocyanate and TEA affords the bicyclic compound (V) and other isomers. Compound (V) is isolated from the mixture and then hydrogenated with H2 over PtO2 in MeOH and a catalytic amount of HCl to provide amine (VI). Reaction of (VI) with acetic anhydride gives the acetamide (VII), which is Boc-deprotected with ethereal HCl yielding amine (VIII). The guanylation of (VIII) with pyrazolecarboxamidine hydrochloride (IX) and DIEA affords the guanidino derivative (X), which is finally hydrolyzed with NaOH to the desired (1S,2S,3R,4R,1'S)-diastereomer. A former DVC Chem 226-227 student cyclized artemisinic acid and obtained artemisinin. The measured optical rotation of the product was [∝]20 = -7.6°, c = 0.5, methanol.
Bonus Question: A plant called annual wormwood, Artemisia spp., has been used in China by apothecaries and herbalists for more than a thousand years to treat many diseases including malaria. The drug’s local name is Qinghaosu (青蒿素) The
biologically active component is a single steroisomer, artemisinin, which is the d- isomer. It can be purchased optically pure from Sigma-Aldrich: [∝]20 = +76.0°, c = 0.5, methanol.
benzodioxepin-10(3H)-one How many stereocenters are present in artemisinin? __________ How many stereoisomers are possible? __________ Identify two different functions in the molecule. ____________________ ____________________ In 2006, a UC Berkeley research team led by Jay Keasling published an article, Nature, 440, 940-943 (13 April 2006), reporting the bio-engineering of a microbe, Saccharomyces cerevisiae, that produces artemisinic acid, which can easily be reacted to produce artemisinin at an estimated cost of ~ 2.5 cents per dose. A former DVC Chem 226-227 student cyclized artemisinic acid and obtained artemisinin. The measured optical rotation of the product was [∝]20 = -7.6°, c = 0.5, methanol. What is the optical purity (enantiomeric excess) of artemisinin in the synthesized sample? ________ Which stereoisomer is in excess? (circle one): d- or l- What is the % of the biologically active stereoisomer present in the sample? _________
Extra credit : Use line drawings to show all of the steps needed to accomplish the synthesis of the following aldehyde. You can use any of the listed lab chemicals. You must begin with acetylene as the starting material, which is inexpensive and available in quantity. Any number of valid chemical reactions are OK.
C
H
O
14. Artemisia has been used by Chinese herbalists for more than a thousand years in the treatment of many
illnesses, including malaria. The earliest record dates back to 200 BC , in the "Fifty two Prescriptions" unearthed from the Mawangdui Han Dynasty Tombs. Its antimalarial application was first described in Zhouhou Beji Fang ("The Handbook of Prescriptions for Emergencies"), edited in the middle of fourth century by Ge Hong. In the 1960s a research program was set up by the Chinese army to find an adequate treatment for malaria. In 1972, in the course of this research, Tu Youyou (Chinese: 屠呦呦)[2] discovered artemisinin in the leaves of Artemisia annua (annual wormwood). The drug is named Qinghaosu (Chinese: 青蒿素) in Chinese. It was one of many candidates then tested by Chinese scientists from a list of nearly 200 traditional Chinese medicines for treating malaria. It was the only one that was effective, but it was found that it cleared malaria parasites from their bodies faster than any other drug in history. Artemisia annua is a common herb and has been found in many parts of the world, including along the Potomac River, in Washington, D.C.
