Practice 4A

7/29/2019 Practice 4A

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Chem 210 Practice Exam 4A

All rights reserved: P. Maslak 2013 Page 1 of 22

Organic Chemistry: Chem 210

Practice Exam 4A

There are 35questions on this exam. The actual exam will be shorter (no more than 30questions). Check that you have done all of the problems and filled in the first 35bubbleson 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 124 points (the actual

exam will be worth 100 points).

InstructionsAnswer sheet

1) On the scantron, you need to clearly fill:

yournameand yourstudent number, section number

Section 001, 12:20 pm lectureSection 002, 3:35 pm lecture

test form (white = test form A; yellow = test form B; blue = test form C, green= test form D).

2) Use a #2 pencil

Exam policy

1)No electronic devices of any kind, such as calculators, cell phones, or even moreadvanced 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 extraneousinformation is used to adjust the scores. Mark your choices with extra care.

7)You may not take the exam with you. You may copy your answers on theprovided page and compare them with the answer key. 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. No partial credit will be given.

3) There is no penalty for guessing.


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Notes: I. When listing reagents, a slash (/) is used between reagents that are employedsimultaneously, 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

OHNo stereochemistry shown(all stereoisomers possible)

Absolute stereochemistryshown

Relative stereochemistryshown (racemic mixture)

Absolute stereochemistry onone 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) On Pluto, where everything is frozen, astronauts discovered two forms of1,2-dibromoethane: gauche and anti. Assuming that there are no rotations around singlebonds, which statement about the two forms is correct?

a) They are enantiomers.

b) They are diastereoisomers.c) They are meso compounds.

d) The gauche form has two stereogenic centers, and the anti has only one.

e) Both will show optical activity.

2. (4 pts) What is the best description of the first organic intermediate formed when 2-butyne reacts with HCl?

a) allylic cation d) vinylic cation

b) allylic anion e) vinylic anionc) chloronium ion


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3. (4 pts) Which of the following will show optical activity?

OH

CO2H

H

HO

CO2H

H

A B

C D

E: 50/50 mixture ofC and D

a) A, D, and E d) A and E onlyb) B, C, and D e) All except Cc) B, C, and E

4. (4 pts) One of the two chair conformations ofcis-1-chloro-3-methylcyclohexane ismore stable than the other by 3.70 kcal/mol. What is the energy cost of 1,3-diaxialinteraction between a chlorine and a methyl group?

a) 3.95 kcal/mol d) 3.05 kcal/mol

b) 2.55 kcal/mol e) 4.85 kcal/molc) 2.80 kcal/mol f) 3.70 kcal/mol


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5. (4 pts) Heating of 2-methylpropene in 60% sulfuric acid gives a mixture of 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene. The best mechanism forthese transformations is:

continued on the next page

H

a)

H

-H+

H2O

H2O

OH

b)

-H+

H+

H2OOH

H

OH

H

OH

H2O


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H

H

H+

H2O

H2O

d)

H H2O

H+

HH2O

c)


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6. (4 pts) What is the final product of the following reaction?

7. (4 pts) Which radical is responsible for the observed selectivity in the chain reactionbelow?

% yield 2% 98%

a) Cl b) Br c) H d) 1o

alkyl radical e) 2o

alkyl radical

Cl-Br

h

Cl

Cl

+

KMnO4/H

excess

OH

O O

O OH

OH

O O

O O

a) b)

c) d)

OH

O O

O

O

OH

O

O OO


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8. (4 pts) Consider1,4 - addition of HCl to methyl-substituted butadienes:

and

I II

The possible 1,4 adducts are listed below:

Cl

A B C D

Select the major 1,4-product for each diene:

Diene I Diene II

a) A Cb) A Dc) B Cd) B D

9. (4 pts) What is true about the following equilibrium?

a) It will be almost completely shifted to the left.b) It will be almost completely shifted to the right.

c) The equilibrium constant is very close to one.d) The equilibrium constant is zero.

Cl

ClCl

H + H3C H

H

H+ H3C C

K

K


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Questions 10and 11 refer to the following reaction:

10. (4 pts) What is the mechanism of the above reaction?

a) SN1 d) E2

b) SN2

e) none of the abovec) E1

11. (4 pts) What happens to the reaction rate if the concentration of t-butoxide isdoubled?

a) no change d) tripled

b) halved e) quadrupledc) doubled f) it depends on the extent of ion pair participation

12. (4 pts) For the following multistep synthesis, which set of reagents would be morelikely to give the desired product?

a) (i) HBr, (ii) O3 followed by Zn/H+, (iii) Li/NH3

b) (i) NaNH2/NH3 followed by CH3CH2I (ii) Lindlars catalyst/H2

(iii) OsO4 followed by NaHSO3

c) (i) H2/Pd/C (1 equivalent), (ii) NaNH2/NH3 followed by CH3CH2Br,

(iii) KMnO4/

OH/H2Od) (i) HgSO4/H2O/H2SO4, (ii) Lindlars catalyst/H2, (iii) OsO4

followed by NaHSO3

H3C Br

H H

HH3C

H D

O K

OH

DCH3CH2

H3C H

CH3CH2CH2C CHCH

3CH

2CH

2CH

OH

CHCH2CH

3

OH(i) (ii) (iii)


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13. (4 pts) Consider the following transformation:

What reagents could be used to carry out this synthesis?

Step 1 Step 2

a) HBr/ether NaNH2/NH3

b) Br2/CCl4 NaOCH3/CH3OH

c) NBS/h NaOH, heatd) NBS/DMSO/H2O PBr3 followed by HCle) a and b would work

f) b and c would work

g) c and d would work

14. (4 pts)What is the product of dehydrohalogenation of (R,R)-2,3-dibromobutane?

CH3

H

H3C

Br

CH3

H

Br

H3C

H

CH3

H3C

H

CH3

H

H3C

H

Br

H

H3C

H3C

a)b) c)

d) e)

1 2


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15. (4 pts) Consider the changes in the UV absorption of butadiene as it undergoes

rotation about the central bond as shown ( = angle of rotation)..

Which graph best approximates the changes in the max as a function of.

rotate


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16. (4 pts) Esterification (shown below) is a reaction converting a carboxylic acid to itsester. It involves only the carbonyl carbon. Esterification of (-)-lactic acid withmethanol yields (+)-methyl lactate. Assuming that there are no side reactions,

what is true about this reaction?

a) An SN2 process has occurred, inverting the absolute configuration of the chiral center.

b) An SN1 reaction at the chiral center has inverted the optical rotation.c) A diastereomer has been produced; diastereomers have different physical properties,

including optical rotation.d) Optical rotation is not directly related to absolute configuration, so the change in signof rotation is merely a coincidence.

17. (4 pts) For the following series of reactions, what is the absolute configuration of thechiral centers in the major product(s)?

a) 1S2S d) 1S2Rb) 1R 2R e) 50% 1S2R and 50% 1R 2Sc) 1R 2S f) 50% 1S2Sand 50% 1R 2S

18. (4 pts) Which of the following statements about the reactivity-selectivity principle iscorrect?

a) Intermediates involved in exergonic reactions are more selective than the same

intermediates involved in endergonic reactions.b) Intermediates involved in exergonic reactions have later transition states than thesame intermediates involved in endergonic reactions.

c) Intermediates involved in exergonic reactions are less reactive than the sameintermediates involved in endergonic reactions.

d) Intermediates involved in exergonic reactions are less selective than the sameintermediates involved in endergonic reactions.

OH

O

OH

OCH3

O

OH

CH3OH

HCl

(-) (+)

H3CC CHD2

Lindlar'scatalyst

Br2

CCl4

product(s)


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19. (4 pts) Which of the following heterocycles is not aromatic? Note that loneelectron pairs are not shown explicitly.

NN

N

BN

BN

B

NP

N

PN

P

N

As

a) b) c) d)

20. (4 pts) Which is the best IUPAC name for the following structure?

H

a) (S)-E-3,6-dimethyl-8-nonyn-2-eneb) (R)-E-4,7-dimethyl-7-nonen-1-ynec) (R)-E-3,6-dimethyl-8-nonyl-1-ened) (S)-Z-4,7-dimethyl-7-nonen-1-ynee) (R)-Z-4,7-dimethylnonan-7-en-1-yne

21. (4 pts) Which of the following compounds is most stable?

a) (1S, 3R)-1-t-butyl-3-methylcyclohexaneb) (1S, 3S)- 1-t-butyl-3-methylcyclohexanec) trans- 1-t-butyl-3-methylcyclohexaned) (1R, 3R)- 1-t-butyl-3-methylcyclohexane

22-25(2 points each) Which reaction in each pair shown below will show the faster rateof disappearance (consumption) of substrate (starting material)?

22. (2 pts)

(CH3)3CBrH2O

EtOH

EtOH(CH3)3CBr

a)

b)


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23. (2 pts)

24. (2 pts)

25. (2 pts)

Cl CH3S-

(CH3)2CHS

-

Cl

c)

d)

e) Br-CN

-CNIf)

g)Br

H2O

H2OBrh)


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26and 27. (2 points each) When 2-bromo-2,3-dimethybutane reacts with any of the basesshown below under E2 conditions, two alkenes are produced: 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene.

26. (2 pts) Which one of the bases shown above would produce the highest yield of2,3-dimethyl-1-butene?

27. (2 pts)Which one of the bases shown above would produce the highest yield of2,3-dimethyl-2-butene?

28and 29. (2 pts each) Fill in the blanks with one of the orbitals listed below to providethe best (most precise) meaning to the following two sentences.

From Streitwieser, Heathcock, and Kosower, 4th

edition:

In an SN2 reaction the donor is the entering nucleophile whose HOMO is a___28______. The acceptor is the organic substrate whose LUMO for the reaction is a___29______ involving the leaving group.

a) orbitalb) * orbital

c) orbitald) * orbital

e) lone-pair orbital

a) CH3CH2O-

b) CH3CH2CO-

CH3

CH3

c) CH3CO-

CH3

CH3

d) CH3CH2CO-

CH2CH3

CH2CH3


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30.(4 pts)Select the best method for preparation of the following compound:

OH

CH3

a) react cyclohexanone with CH3Lib) react 1-methylcyclohexene with Hg(OAc)2 followed by NaBH4c) react cyclohexene with BH3; NaOH/H2O2, followed by CH3Brd) react cyclohexene with MCPBA, followed by CH3MgBre) react 1-methylcylohexene with KMnO4/NaOH

31. (4 pts) When 1,3,9-tribromo-9-methyl-5-decanol is treated with base it can form threecyclic ethers by an SN2 reaction. Which one will form fastest?

O

Br

BrO

Br

Br O

Br

Br

a) b) c)

32. (4 pts) Which is the best sequence of reactions for preparation of 2,4-dinitrobenzoic acidfrom benzene?

a) 1. HNO3/H2SO4 2. CH3Br/AlCl3 3. HNO3/H2SO4 4. KMnO4/H+b) 1. CH3Br/AlCl3 2. HNO3/H2SO4 3. KMnO4/H

+4. HNO3/H2SO4

c) 1. CH3Br/AlCl3 2. KMnO4/H+

3. HNO3/H2SO4 (excess)

d) 1. HNO3/H2SO4 2. CH3Br/AlCl3 3. KMnO4/H+

4. HNO3/H2SO4

e) 1. CH3Br/AlCl3 2. HNO3/H2SO4 (excess) 3. KMnO4/H+


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33. (4 pts) Compound A was treated with a large excess of CH3MgBr. The resulting productwas exposed to POCl3/pyridine to give compound B, as one of many products.

B

Which of the following compounds can be A?

OO

H

O

H

OO

O

O

O

O

O

O

O

O

O

O

OO

a) b)

c) d)


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34. (4 pts) Oxidation of 1o alcohols with CrO3/H2SO4/H2O/acetone produces carboxylicacids. Oxidation of 1

oalcohols with pyridinium chlorochromate in a dry solvent

(e.g., CH2Cl2) produces an aldehyde. Which of the following is true?

a) The initial product of oxidation is always the carboxylic acid when using

CrO3/H2SO4/H2O/acetone.

b) The initially formed product of CrO3/H2SO4/H2O/acetone oxidation can

undergo a second E2-like elimination of the chromate derived from thehydrated aldehyde.

c) Pyridinium chlorochromate oxidations always stop at the aldehyde, regardlessof conditions.

d) Pyridinium chlorochromate in an anhydrous solvent prevents the aldehydefrom forming the hydrate. Therefore, further oxidation cannot take place.

e) a and c

f) b and c

g) b and d

35. (4 pts) Which of the following series of reactions is the best way to convert R-2-pentanol to R-2-ethoxypentane?

a) p-TosCl/pyridine; EtOH/NaOHb) p-TosCl/pyridine; PBr

3/ether; NaOEt/EtOH

c) PBr3/ether; NaOEt/DMSO

d) EtOH/NaOH; HCle) HBr; NaOEt/EtOH

end of the exam


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Total Strain Energies in Cycloalkanes

ring size kJ/mol kcal/mol

3 115 27.64 110 26.45 27 6.56 0 07 26 6.38 40 8.6

Energy Costs for Interactions in AlkaneConformers

Interaction kJ/mole kcal/mole

H-H eclipsed 4.0 1.0

H-CH3 eclipsed 6.0 1.4

CH3-CH3 eclipsed 11.0 2.6CH3-CH3 gauche 3.8 0.9


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Selectivity of halogen radicals (perH)

3o 2o 1oF 2 1 1Cl 5 3.5 1Br 1600 80 1I 97000 1100 1


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All rights reserved: P Maslak 2013 Page 22 of 22

ANSWER KEY: 4A

1. B 4 pts

2. D 4 pts

3. A 4 pts4. B 4 pts

5. C 4 pts

6. C 4 pts7. B 4 pts

8. A 4 pts9. A 4 pts

10. D 4 pts

11. C 4 pts12. B 4 pts

13. F 4 pts

14. B 4 pts

15. C 4 pts16. D 4 pts

17. E 4 pts

18. D 4 pts19. C 4 pts

20. B 4 pts

21. A 4 pts22. A 2 pts

23. C 2 pts

24. F 2 pts

25. G 2 pts26. D 2 pts

27. A 2 pts

28. E 2 pts29. B 2 pts

30. D 4 pts

31. B 4 pts

32. E 4 pts33. B 4 pts

34. G 4 pts

35. C 4 pts

Practice 4A

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