Name: _________________
Chem 226 / Fall 2012
Lab Section: Circle one.
MW(11:00) or MW(2:30)
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. Which compound can have four stereoisomers? (Be sure to consider E- & Z- diastereomers.)
A)
B)
C)
D)
5-bromo-2,4-dimethyl pentene
5-bromo-3,4-dimethyl-2-pentene
1-bromo-2,4-dimethyl-2-pentene
2-bromo-3,4-dimethyl pentene
2. A reaction mixture consisted of 0.5M methyl iodide and 1.0 M sodium hydroxide. The measured rate of reaction
at room temperature was 0.05 mol/L per second. What would be the predicted rate for a reaction mixture of 1.0
M methyl iodide and 2.0 M sodium hydroxide?
A.
B.
C.
D.
E.
0.05 mol/L per second
0.20 mol/L per second
0.10 mol/L per second
0.25 mol/L per second
0.50 mol/L per second
3. The most stable chair conformation of cis-1-tert-butyl-2-methylcyclohexane has
A.
B.
C.
D.
both groups equatorial.
both groups axial.
the tert-butyl group equatorial and the methyl group axial.
the tert-butyl group axial and the methyl group equatorial.
4. Consider the molecule below. What is the maximum number of methyl groups that can be in the equatorial
position at the same time?
A. 0
B. 1
C. 2
D. 3
E. 4
5. In the dehydrohalogenation of 2-bromobutane, which conformation below leads directly to the formation of cis2-butene?
A.
B.
C.
D.
E.
only I
only II
only III
I and II
none
6. Which of the following cannot undergo an E2 reaction?
A.
B.
C.
D.
E.
only I
only II
only III
I and III
none
7. Consider the SN1, SN2, E1, and E2 mechanisms. The energy diagram shown below corresponds to
A.
B.
C.
D.
only the SN1 mechanism.
only the SN2 mechanism.
both the SN1 and E1 mechanisms.
both the SN2 and E2 mechanisms.
8. Consider the reaction coordinate/ energy diagram shown below. 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 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.
B)
9. Which of the following molecules are chiral?
A.
B.
C.
D.
E.
only II
only III
II and III
I, II, and III
none
10. How many of the following three molecules respectively have chiral centers, and how many are actually chiral
molecules?
HO
HO
HO
H
O
C OH
C H
C OH
OH
C OH
OH
C
C
C OH
C OH
O
H
C
F
H
Cl
O
C
H C
H C
C
O
OH
OH
OH
OH
A. 3, 3
B. 3, 2
C. 2, 2
D. 2, 1
E. 3, 1
11. A pure sample of an amino acid (+)-(S)-phenylalanine, which has a specific rotation of +70o, is reacted with a
racemic mixture of the analgesic ibuprofen to produce two diastereomeric salts, (+, +) and (+, -). The (+, -)
C
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.
B.
C.
D.
E.
95% S, 5% R
90% S, 10% R
55% S, 45% R
52.5% S, 47.5% R
Cannot determine
12. The following structures represent:
A. same molecules
B. enantiomers
C. diastereomers
D. different molecules
E. constitutional isomers
13. The four isomeric dimethylcyclopropanes are shown below. Identify two of the isomers which are related as
diastereomers.
A.
B.
C.
D.
I and III
I and IV
II and III
III and IV
14. Which of the following Fischer projections corresponds to the compound shown below?
15. Which of the following carbocations is (are) likely to undergo a rearrangement?
A.
B.
C.
D.
only I
I and III
II and III
I, II, and III
16. Rank the following from slowest to fastest for solvolysis in ethanol/water?
A) II < III < I < IV
B) II < III < IV < I
C) I < IV < III < II
D) I < II < III < IV
17. Which prediction is most likely correct for the ranking of the following solvent systems in decreasing order of
reactivity under Sn1 reaction conditions?
I) 50%:50% ethanol:water
A.
B.
C.
D.
E.
II) 50%:50% methanol:water
III) water
IV) 50%:50% acetone:water
III > IV > II > I
IV > III > II > I
II > III > IV > I
III > II > I > IV
II > IV > III > I
18. Rank the following substrates in decreasing order of reactivity under Sn2 reaction conditions:
I) methyl bromide
A.
B.
C.
D.
E.
II) 1-chloropropane
III) 1-chloro-2,2-dimethylpropane IV) methyl iodide
I > IV > II > III
IV > III > II > I
II > IV > I > III
III > IV > II > I
IV > I > II > III
19. Which one of the following descriptions correctly fits the substitution reaction below? (The product is a Fisher
projection.)
Likely mechanism
Rate expression
Stereochemistry
20. Which of the following does not give 1,2-dimethylcyclohexene as one of the acid-catalyzed dehydration
products?
End of Multiple Choice
True (A)/ False (B): Answer on Scantron
21. If a molecule has only one stereogenic center it must be chiral.
22. The structures below have opposite optical rotations, one levo and one dextro.
23. An optically active (+)-R-alcohol isomerizes in acid to produce a mixture which has []20 = 0°. This is because
all of the starting alcohol has been converted to the opposite enantiomer.
24. Bimolecular reactions have at 2 Transition States.
25. The following mesylates react with sodium iodide in acetone. The relative rates from the fastest to the slowest
are: II > I > III > IV .
26. The following arrows and illustration show the correct electron movements and transition state’s
stereochemical arrangement for an E2 reaction mechanism.
27. The biochemical conversion of norephedrine to adrenalin is similar to an Sn2 reaction.
28. In the following reaction, a kinetics experiment was conducted where a 25 mL solution, which had
respectively 5 mmol of bromide and 5 mmol of sodium hydroxide, reacted in 15 sec. It is expected
that if the volume of the solution were doubled and the # of moles kept the same, the reaction would
take place in about 30 sec.
29. The slow, rate-determining step, in the acid-catalyzed dehydration of 2-methyl-2-propanol is the loss of water
from the oxonium ion to form a carbocation.
30. The following Fisher structures are respectively R- and S- enantiomers.
End of True/ False
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.
32. [3pts] The following thermodynamic data were obtained for experimental oxidation of 3 different alkenes with
the same mole cular formula. Match the structures to the data.
Compound
A)
B)
C)
____ (Z)-2-pentene
Heat of Reaction (kJ/mol)
-186
-164
-162
____ 2-methyl-2-butene
____ (E)-2-pentene
33. [3pts] Circle the stronger nucleophile in each pair:
NH3 vs. PH3
I- vs. Cl-
CH3OH vs. CH3O-
34. [10pts] Complete the mechanism for the following reaction. Draw structures for the two intermediates. Use
arrows for the electron movement to show each step in the formation of the alkene. Use water in the last step.
Draw an energy diagram below illustrating the reaction: EaI = +25kJ; ΔHI = +10kJ; EaII = +10kJ; ΔHII = +5kJ ;
EaIII = +5kJ; ΔHRxn= -25kJ
35. [10pts] Peramivir is a relatively new antiviral drug. The active stereoisomer and the IUPAC name are shown
below. It was developed by BioCryst Pharmaceuticals in collaboration with Green Cross Pharmaceuticals in
South Korea and Shionogi Pharmaceuticals in Japan. It is approved for treatment of H1N1 influenza by the
U.S. Food and Drug Administration.
*
(+)(1S,2S,3S,4R)-3-[(1S)-1-acetamido-2-ethyl-butyl]-4-(diaminomethylideneamino)-2-hydroxycyclopentane-1-carboxylic acid;
/ []20 = +57°, c = 0.5, ethanol
Peramivir is an enzyme 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, which are presently in
use.
How many stereocenters are present in peramivir?
How many stereoisomers are possible?
__________
__________
Identify three different functions in the molecule. (Name them below, circle and number them in the
structure above.)
1) ____________________
2) ____________________
3) ____________________
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
on-line. 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 lWhat is the enantiomeric excess of the main stereoisomer of peramivir in the synthesized sample?
________
Which stereoisomer is in excess? (circle one): d- or lWhat is the % of the biologically active stereoisomer present in the sample?
_________