Practice 3A
Practice 3A
Practice 3A
Practice Exam 3A
Practice Exam 3A
There are 28 questions on this exam. Check that you have done all of the problems and filled in the first 28 bubbles on the scantron. Most questions are worth 4 points; there are several two-point questions clearly labeled in the text. The maximum score on this exam is 100 points. Instructions Answer sheet 1) On the scantron, you need to clearly fill: your name and your student number, section number: (it is 001) test form (white = test form A; yellow = test form B). 2) Use a #2 pencil Exam policy 1) No electronic devices of any kind, such as calculators, cell phones, or even more advanced digital watches, are allowed. Possession of such devices during the exam, whether in use or not, is grounds for awarding a zero on the exam. 2) Molecular models are allowed (no instruction pages are permitted, however). 3) There are some blank pages at the end of the test that can be used as scratch paper. 4) Relevant tables, including the periodic table, are attached at the end of this exam. 5) Numerical values given in one question apply only to that question, and should not be used in other questions, unless there is a specific instruction to do so. If necessary, the values from the provided tables should be used, even if they differ from values that you may remember from different sources. 6) The exam results are based strictly on scantrons marks. No extraneous information is used to adjust the scores. Mark your choices with extra care. 7) Feel free to take this copy of the exam with you. The answer key will be posted on the web after the exam (under "News"). Hints 1) As you read the question, underline or circle key words to highlight them for yourself. 2) Questions have only one correct answer, unless indicated otherwise. No partial credit will be given. 3) There is no penalty for guessing.
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Chem 210
Practice Exam 3A
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
Br
Br
Br
OH
No stereochemistry shown (all stereoisomers possible)
OH
Absolute stereochemistry shown
OH
Relative stereochemistry shown (racemic mixture)
OH
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. (4 pts) Radicals can be compared according to their selectivity in hydrogen abstractions based on the reactivityselectivity principle. Which of the following radicals would be expected to have selectivity very similar to that of the H radical? a) Cl b) F c) HO d) Br e) I
2. (4 pts) Which of the following MO energy diagrams corresponds to the cyclopropenyl anion?
a)
b)
c)
d)
e)
3. (4 pts) Which of the following is the best characterization of the cyclopentadienyl cation?
a) antiaromatic
b) non-aromatic
c) carbocatatonic
d) aromatic
e) hyperconjugated
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Chem 210
Practice Exam 3A
4. (4 pts) Which of the following is (are) the product(s) of the reaction shown below?
Br2 H2O Br CH3 OH CH3 A B CH3 Br CH3 OH C CH3 Br OH CH3 D Br CH3 CH3 OH
a) A
b) B
c) C
d) D
e) A and B
f) C and D
5. (4 pts) How many stereoisomers of the product will form in this reaction?
1. OsO4 2. NaHSO3
a) 1 b) 2 c) 3 d) 4 e) 5
6. (4 pts) Which of the reagents shown below would accomplish the following transformations?
Br 1. A 2. B OH
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Chem 210
Practice Exam 3A
7. (4 pts) Surprisingly, the reaction shown below goes through a bromonium ion. What is (are) the major product(s) of this reaction?
Br + HBr
A: B: C: D: a) A b) B c) C
d) D
8-10. (2 pts each) Here is a retro-synthetic analysis for the preparation of propanal from 3-hexyne. What are the most appropriate reagents to accomplish each step of the synthesis of propanal?
HO
OH
10 H
propanal
d) OsO4;NaHSO3 + h) H3O
11. (4 pts) Which of the following compounds was the starting material for the oxidation shown below?
O ?
KMnO4/H+
HO O O OH
OH
CO2
a)
b)
c)
d)
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Chem 210
Practice Exam 3A
O
a) BH3-THF; H2O2/NaOH d) OsO4; NaHSO3 b) H2SO4/H2O e) O3; Zn/AcOH c) HgSO4/H2SO4/H2O f) HIO4/H2O/THF
13. (4 pts) Carbocation A can be an intermediate in many reactions studied in Chem 210. Which of the following reactions does not involve A as an intermediate?
A
a) electrophilic addition of HBr to 2-butyne b) electrophilic addition of HCl to 1,2-butadiene c) electrophilic addition of HI to 1,3-butadiene d) rearrangement of 3-bromo-1-butene (the kinetic product) to 1-bromo-2-butene (the thermodynamic product) e) reaction of 3-hydroxy-1-butene with H2SO4 to yield 1,3-butadiene
14-16. (2 pts each) An unknown hydrocarbon A, with formula C6H12, reacts with 1 molar equivalent of H2 over a Pd catalyst. Hydrocarbon A also reacts with OsO4 to give a diol, B. When oxidized with KMnO4 in acidic solution, A gives 2 fragments. One fragment is propanoic acid, CH3CH2COOH, and the other is a ketone, C. From the structures (a)-(j) below, select the correct answers for questions 14-16. 14. What is the structure of A? 15. What is the structure of B? 16. What is the structure of C?
OH
OH
O H OH OH c) d) e)
a)
b)
OH O
OH
f)
g)
h)
i)
j)
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Chem 210
Practice Exam 3A
17. (4 pts) Consider the following synthesis. What is wrong with these transformations?
H2B BH3-THF BH2 H2O2, NaOH O
a) BH3 in THF is actually unreactive toward alkynes. b) BH3 should add to adjacent carbons, rather than the same carbon. c) The oxygen in THF is responsible for oxidation; H2O2 and NaOH are not required. d) Borane can be used as an electrophile only with non-terminal alkynes. e) The borane addition follows regiochemistry opposite to that shown. 18. (4 pts) All six MOs of benzene are shown below in a random order, in a view from the top (i.e. only top lobes of p orbitals on carbon atoms are visible). Which of the following electronic transitions will correspond to the absorption band with the shortest wavelength?
a)
E F
b) A B
c)
E B
d) C F
e)
C B
19. (4 pts) What is the absolute configuration of the stereogenic centers in the product(s) of the following reaction?
CH3 H + Br2 1,2-dibromo-3-methylcyclohexane
20. (4 pts) In which of the following solvents is it possible to create acetylide anions? a) AcOH b) H2O c) H3COH d) (i-Pr)2NH e) t-BuOH
21. (4 pts) (R)-2-fluorobutane undergoes free-radical chlorination with Cl2. Including stereoisomers, how many monochlorinated substitution products will form? a) 3 b) 4 c) 5 d) 6 e) 7 f) 8
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Chem 210
Practice Exam 3A
22. (4 pts) The following transformation is carried out in three steps. What are the appropriate reagents for the first (I) step? H OH I II III H HO H a) H2/Lindlar catalyst b) NaNH2/NH3 (liquid); CH3CH2Br c) O3; Zn/AcOH d) KMnO4/NaOH e) HCCH/NaNH2/THF/CH3I f) H2/Pd/C g) Li/NH3 (liquid) h) NBS/DMSO/H2O
23. (4 pts) Consider the following transformation in which a cyclic bromoether is formed, rather than the expected bromohydrin. Which of the electron-pushing scheme best represents the mechanism of this reaction?
O OH Br2, H2O -HBr Br
a) Br H O
b) Br
c) Br
d) H
H O
Br
e) Br
O H
O H H
24. (4 pts) Assuming that only monosubstitution products are formed in the reaction shown below, what would be the expected ratio of 2o to 3o chlorides?
Cl2 h
a) 3/1 b) 6/7 c) 3/2 d) 21/10 e) 15/17
25. (4 pts) In the molecule shown below selected C-H bonds are labeled with capital letters. Arrange these bonds according to the difficulty with which they would be broken in radical-forming reactions, starting with the strongest.
H H D H A H C CH3 H B
a) e)
B>D>A>C D>B>A>C
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Chem 210
Practice Exam 3A
NBS h, CCl4
OH Br Br OH Br A B C D Br
a) A
b) B
c) C
d) D
e) A and B
f) C and D
27. (4 pts) Consider only the following two major products of the addition reaction shown below. Which statement is true about this reaction?
Br + HBr +
Br
a) The major product formed under thermodynamic control is 4-bromo-4-methyl-2-pentene. b) The major product formed under kinetic control is 4-bromo-2-methyl-2-pentene. c) The major product formed under thermodynamic control is 4-bromo-2-methyl-2-pentene. d) The 1,2adduct is the kinetic product and the 1,4-adduct is the thermodynamic product. e) There is no thermodynamic or kinetic control in this reaction.
28. (4 pts) On reaction with acid, 4-pyrone is protonated to give a very stable cationic product. Which of the following structures shows the protonation site in that product?
O 4-pyrone O H d)
a)
O H H O
b)
c)
e)
H H
O H
Chem 210
Practice Exam 3A
Total Strain Energies in Cycloalkanes ring size kJ/mol kcal/mol 115 27.6 3 110 26.4 4 27 6.5 5 0 0 6 26 6.3 7 40 8.6 8
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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Chem 210
Practice Exam 3A
F Cl Br I
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Chem 210
Practice Exam 3A
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Chem 210
Practice Exam 3A
Answer Key: 3A 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. A C A F B D C A D J B C A C D F E B H D D B B D A F C C
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