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Chem 210 Training Set III
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Organic Chemistry: Chem 210
Training Set III
The questions are arranged approximately in the order of the coverage of material in the lecture. This set covers the material of the third exam.
Notes: I. When listing reagents, a slash (/) is used between reagents that are employed
simultaneously, and a semicolon (;) is used between reagents that are employed in a stepwise fashion.
II. The stereochemistry conventions are illustrated below:
Br
OH
Br
OH
Br
OH
Br
OH No stereochemistry shown
(all stereoisomers possible) Absolute stereochemistry shown
Relative stereochemistry shown (racemic mixture)
Absolute stereochemistry on one center, unspecified
stereochemistry on the other
III. Abbreviations: Me = methyl, Et = ethyl, Pr = propyl, Bu = butyl, Pe = pentyl, Ph = phenyl (i.e. benzene as a substituent), AcO = acetate (H3CCOO), MCPBA = m-chloroperbenzoic acid., TosO = TsO = tosylate
1. In the polar reaction of vinyl chloride with HBr the only product formed is 1,1-
bromochloroethane (not 1-bromo-2-chloroethane):
ClCH=CH2 + HBr ClBrCHCH3 (not: ClCH2CH2Br) What is the best explanation for this preference?
a) The electrophile prefers to add to the chlorine-substituted carbon. b) Chlorine is causing steric hindrance for the addition of the bromine. c) The bromine electrophile is attracted to the lone electron pairs on chlorine. d) The two possible carbocations formed have the same stabilities, but 1,1-
bromochloroethane is much more stable than 1-bromo-2-chloroethane. e) The carbocation formed by protonation on the unsubstituted carbon is stabilized
by resonance. f) A bromonium ion prevents attack on the carbon bearing the chlorine.
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2. The molecule of I-N3 adds to alkenes by an electrophilic mechanism similar to that of
Br2. Taking into account the relative electronegativity of I (2.5) and N (3.0), and the fact that N3
– is a stable anion, which of the compounds listed is the product of the following reaction?
3. What is the product of the following reaction?
Br2
H2O
OH
Br
H3C
a) b) c) d)
OHH3C
Br
BrH3C
OH
BrH3C
OH
4. Which of the following is not a redox reaction?
CH3
I-N3
I N3
H CH3
N3 I
H CH3
H N3
I CH3
H I
N3 CH3
a)
?
b) c) d)
e) f)
N3 H
I CH3
I H
N3 CH3
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5. When 4-penten-1-ol is treated with aqueous bromine, a cyclic bromo-substituted ether is formed rather than the expected bromohydrin. Select the explanation that best accounts for this result.
a) The ether is the result of a hydride shift in the initially formed carbocation. b) The ether is formed in the intramolecular nucleophilic attack on the initially
formed bromonium ion. c) The reaction is initiated by the protonation of the system by the –OH group. d) The ether is formed by a nucleophilic attack of the bond on the –OH group. e) The initially formed bromonium ion undergoes an alkyl shift to form new C-O
bond. f) Before any addition to the double bond, the –OH group is replaced by –Br.
6. We have discussed three ways to convert alkenes to alcohols: (A) acid-catalyzed
hydration, (B) hydroboration-oxidation, and (C) oxymercuration-demercuration. Which of the following statements about these reactions is incorrect?
a) B results in the syn stereochemistry of the -H and -OH groups, while A and C
show no clear stereochemical preference. b) A and C give Markovnikov products, while B results in anti-Markovnikov
regioselectivity. c) Carbocation rearrangements are observed for A, but unrearranged products are
obtained from B and C. d) In all three reactions water serves as a nucleophile. e) In A a Brønsted acid is the electrophile, while in B and C Lewis acids play that
role. f) B and C require consecutive additions of different reagents or catalysts, while in A
only one reagent or catalyst is required. g) In B and C compounds of boron are involved, while in A no boron-derived
chemicals are required. 7. Which of the compounds listed will result from the following reaction?
OHO
BrBr2
H2O
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8. What is the best description of the mechanism of the following transformation?
9. Which of the compounds listed is the product of the following reaction?
OH OHH+
-H2O
O
OH OH H+
H2O
OOH OH2 OH OH
OH2
O
H2O
H+OH O H
OH2
HO OH2 O
H2O
H+OH OH
OH2
OHOH OH2 O
H2O
H+OH OH O
H
-H2O
-H2O
OH O-HO-
OH2
-H2OO
H2O
H
-H2O
a)
b)
c)
d)
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10. Which of the following will react with periodic acid (HIO4) to give an aldehyde product?
11. Compound A reacts with ozone (O3) to produce compounds I and II. Which structure
could be compound A? 12. Compound B has a molecular formula of C6H12. It reacts with KMnO4to produce two
identical ketones. It reacts with ozone (O3) to produce the same two products. What is the structure of compound B?
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13. Which of the following C11H16 hydrocarbons will not produce the carbonyl
compounds shown below when treated with ozone?
14. Which compound can most easily undergo elimination to give an alkyne? 15. Alkyne hydrogens are more acidic than alkene or alkane hydrogens because:
a) The lone pair on alkyne carbon has higher s character. b) The anion formed is more stable. c) The electrons in the sp orbital are closer to the nucleus. d) All of the above.
16. Which reagents will give the following product?
a) H2/Pd/C b) H2/Lindlar’s catalyst c) Li/NH3 d) H+/H2O
C11H16
1) O3
2) Zn/AcOH O O O
H H
O O
H2CO+ +
a) b)
c) d) e)
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17. Selected bond angles for five hydrocarbons are shown below. Arrange these hydrocarbons according to their pKa values, from the lowest to the highest. Assume that the structures of the corresponding conjugate bases are very similar to the hydrocarbons.
a) E<B<D<C<A e) A<C<D<B<E b) D<A<B<C<E f) E<C<B<A<D c) B<D<A<E<C g) C<E<A<D<B d) E<D<C<B<A h) A<B<C<D<E
18. Which reagents would be best to perform the following reaction?
a) BH3; NaOH/H2O2 b) HgSO4/H2O/H2SO4 c) NaNH2; CH3I; HgSO4/H2O/H2SO4 d) OsO4; HIO4
19. Which of the following synthetic schemes may be used to prepare the molecule
shown below?
a) React acetylene with NaNH2/NH3; add half of an equivalent of 1,4-dibromobutane; then add H2O/H2SO4/HgSO4
b) React acetylene with NaNH2/NH3; add one equivalent of 1,6-dibromohexane; then add BH3·THF followed by –OH/H2O2.
c) React 1,6-octadiene with O3 followed by Zn/AcOH d) React 1,2-dimethylcyclohexene with KMnO4/H
+ e) React cyclooctene with OsO4/pyridine; NaHSO3 followed by HIO4 f) Both (a) and (b) may work g) Both (a) and (d) may work h) Both (b) and (e) may work i) Both (c) and (e) may work
H
HHH
109.5oH
H115o H H
HH
117o
HH
180oH
HH
H
108o
128o
EDCBA
O
O
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20. What reagents (and in what sequence) would you use to carry out the following reaction?
a) (1) Cl2/h followed by KOH, (2) Br2/CCl4 followed by KOHb) (1) Br2/heat followed by KOH, (2) NBS/DMSO/H2O followed by KOHc) (1) KOH followed by Br2/heat, (2) Br2/CCl4 followed by KOH d) (1) KOH followed by Br2/H2O, (2) HBr followed by KOH e) (1) Cl2/h followed by NaOH, (2) HBr followed by KOH f) (1) Br2/H2O followed by NaOH, (2) Br2/H2O followed by NaOH g) (1) Br2/h followed by NaOH (2) OsO4/NaHSO3 followed by HBr
21-24. From the list below (a-j), select the appropriate reagent(s) for each step (21-24) of
the following transformation:
a) PBr3 f) Br2/CCl4 b) BH3·THF followed by –OH/H2O2 g) NaNH2 c) HgSO4/H2O/H2SO4 h) H2/Lindlar’s catalyst d) HBr/ether i) NaNH2/NH3 and PhCH2Br e) NaNH2/NH3 and PhCCH j) O3 followed by Zn/H+
25. Which of the reaction conditions would be best to perform the following reaction?
a) HBr (1 equivalent); Br2 b) HBr (2 equivalents); Br2/h c) Br2 (2 equivalents); H2/Pd/C c) Br2 (2 equivalents); NaOH
several steps
Ph21
Ph
Br Br22
Ph
23
PhPh
24Ph Ph
O
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26-33. Each reaction requires a specific set of reagents and reaction conditions. Select the best set of reagents (a-j) for each transformation (26-33). You do not have to use all of the reagents, and you may use some of the reagents more than once.
26. Which reagent will yield a Markovnikov bromide when reacted with an alkene? 27. Which reagent needs to be used to convert a terminal alkyne to a ketone? 28. Which reagent needs to be used to convert a terminal alkyne to an aldehyde? 29. Which reagent will give a cis diol when reacted with a cyclic alkene? 30. Which is the best reagent to produce cis alkenes from alkynes? 31. Which reagent will give two molecules of organic product per each molecule of
alkene reactant? 32. Which reagent will yield an halohydrin when reacted with an alkene? 33. Which reagent will yield an anti-Markovnikov alcohol when reacted with an
alkene?
a) BH3·THF; H2O2/HO– f) KOH b) Hg(OAc)2/H2O; NaBH4 g) OsO4/pyridine; NaHSO3
c) Lindlar catalyst/H2 h) HgSO4/H2SO4/H2O d) O3; Zn/AcOH i) NaNH2; CH3I e) NBS/DMSO/H2O j) HBr/ether
34. Which compound has the lowest wavelength of UV absorption (shortest max)? 35. Which of the following molecules will have a * transition in the 200-400 nm
region?
36. Under thermodynamic control, which of the following products would predominate?
C CH2H2Ca) b) c)
d) e) f)
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37. A reaction under kinetic control depends on:
a) The product stability (G). b) The activation energies (G‡). c) The relative energy of the reactants. d) All of the above.
38. Consider the addition of HBr to 1,3-butadiene. Which of the following statements
about this reaction is incorrect?
a) A and B are formed from the same intermediate. b) In the intermediate, the positive charge on the secondary carbon is larger than the
charge on the primary carbon, resulting in more rapid formation of A. c) In B the double bond is more stabilized by hyperconjugation than in A. d) At higher temperatures B is the major product. e) Under the kinetically controlled conditions A and B can easily interconvert. f) In the starting diene, the HOMO orbital lobes on the terminal carbons are larger
than the corresponding lobes on the internal carbons. g) The first step of the reaction is controlled by the HOMO of the diene, while the
second step is controlled by the LUMO of the intermediate. h) There is only one transition state leading to the intermediate, but two different
transition states leading to the two products. i) All transition states resemble the intermediate more than they resemble starting
diene or the products. 39. Which of the following best describes the MO diagram of the aromatic
cycloheptratriene cation?
HBr
Br
Br+
A B
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40. Which of the following is antiaromatic?
41-42. Questions 41 and 42 concern the conjugated cyclic systems shown below (assume
all molecules are planar):
41. Which compounds are aromatic?
a) A, E, G b) B, C, G c) C, G, F d) C, D, F
e) D, E, F f) A, D, F g) B, E, G
42. Which compounds are antiaromatic?
a) A, B, E, G b) A, B, C, G c) D, E, F, G
d) A, C, E, G e) B, D, E, G f) C, D, E, F
43. Compound A shows a large dipole moment. Which structure(s) should be used to
adequately explain this observation? + +_ _
A B C D
• •
a) A b) B c) C d) D e) B and D 44. Which of the following resonance structures is not aromatic?
A B C
D E F
G
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45. What is the product of the following reaction? 46. Which of the following reactions is not a radical termination step?
47. Which is the least likely product of the following allylic bromination?
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48-51. Questions 48-51 involve use of the following sets of reagents. For each reaction
shown, chose the reagent which would best be used to effect the transformation
shown.
a) PBr3/ether b) HBr/ether c) SOCl2/pyridine
d) NBS/h/CCl4 e) Br2/h f) HCl/ether g) Cl2/h
48. OH Cl
49. HHO BrH
50.
CH3CH2Br
51. CH3 CH3Br
(major product)
52. Only one of the following reactions is likely to work as indicated. Which one?
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53. The radical chain reaction of Cl-Br with 2,3-dimethylbutane gives a mixture of products. Which products (and in what ratio) are formed?
Br
Br=
1600
6
6
5=
Br
Br
6
1600=
Cl
Cl
6=
Cl
Cl5
a)
b)
c)
d)
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Total Strain Energies in Cycloalkanes
ring size kJ/mol kcal/mol3 115 27.6 4 110 26.4 5 27 6.5 6 0 0 7 26 6.3 8 40 8.6
Energy Costs for Interactions in Alkane Conformers
Interaction kJ/mole kcal/mole H-H eclipsed 4.0 1.0
H-CH3 eclipsed 6.0 1.4
CH3-CH3 eclipsed 11.0 2.6
CH3-CH3 gauche 3.8 0.9
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Selectivity of halogen radicals (per H)
3o 2o 1o
F· 2 1 1 Cl· 5 3.5 1 Br· 1600 80 1 I· 97000 1100 1
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Answer key: Set 3
1. E 2. C 3. A 4. A 5. B 6. D 7. D 8. A 9. D 10. B 11. A 12. A 13. D 14. D 15. D 16. B 17. D 18. C 19. G 20. A 21. F 22. G 23. I 24. C 25. A 26. J
27. H 28. A 29. G 30. C 31. D 32. E 33. A 34. B 35. C 36. C 37. B 38. E 39. A 40. A 41. D 42. A 43. C 44. A 45. B 46. D 47. D 48. F 49. A 50. D 51. E 52. D
53. C