Practice 3C

7/29/2019 Practice 3C

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Chem 210 Practice Exam 3C

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Organic Chemistry: Chem 210

Practice Exam 3C

There are 30 questions on this exam. Check that you have done all of the problems and filled in the first30 bubbles on the scantron. Most questions are worth 4 points; there are several two-point questionsclearly labeled in the text. The maximum score on this exam is 100 points.

Instructions

Answer sheet1) On the scantron, you need to clearly fill:

yournameand yourstudent 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 advanceddigital 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 webafter 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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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

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) The following transformation is carried out in three steps (I - III). If the second step involves

hydrogenation, what are the appropriate reagents for the first (I) step?

Br

I I I I I I

HO

OH

OH

OH

a) Br2/H2O b) H2/Lindlar

c) H2SO4/H2O d) Hg(OAc)2/H2O; NaBH4

e) NaNH2/THF f) O3; Zn/AcOH

g) BH3THF; H2O2/NaOH h) KMnO4/OH

2. (4 pts) How many diols, including stereoisomers, are formed, in the following reaction?

Hg(OAc)2 (excess)

H2O

NaBH4

a) 1 b) 2 c) 3 d) 4 e) 6

3. (4 pts) 2-Butyne is allowed to react with Li in NH3(liq). The obtained product is treatedwith Br2 in CCl4. Which of the following compounds is the end result of this sequence

of reactions?

HH3C

Br

Br

CH3H

CH3H

Br

Br

CH3H

HH

Br

Br

CH3H3C

HH3C

Br

Br

HH

HH3C

Br

Br

HH3C

a) b) c) d) e)


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45. Assume that only monochloridesare produced in the following reaction.

Cl2

light

4. (2 pts) Which chloride will be produced in the highest yield?

a) 1-chloro-2-methylbutaneb) 2-chloro-2-methylbutanec) 2-chloro-3-methylbutaned) 1-chloro-3-methylbutane

5. (2 pts) What fraction of the total would 2o chlorides be?

a) 1/6 b) 7/9 c) 5/9 d) 5/21 e) 1/3

6. (4 pts.) Which of the following MO diagrams would best represent planar cyclooctatetraene?

a) b) c) d) e)


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7. (4 pts) How many stereoisomers of the product will form in this reaction?

CH3

O

C H

CH3

H2C

excess H2

Pd/C

?

a) 1 b) 2 c) 3 d) 4 e) 6

8. (4 pts.) Assuming that all non-hydrogen atoms in the planar molecules shown below are sp2hybridized, which molecules are antiaromatic?

N

O

A

N

S

N

B

N

N N

N

C

S

D

O

E

a) A b) B c) C d) D e) D and E

9. (4 pts) Which of the following compounds is among the major products of the following reaction?

CH3

H

1. BH3/THF

2. H2O2, OH

?

CH3

H

H

OH

CH3

OH

H

H

H

OH

H

CH3

CH3

H

BH2

H

CH3

OH

OH

H

a) b) c) d) e)


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10. (4 pts) Which of the following statements about electronic transitions in organic molecules isincorrect?

a) Usually,n* transitions are of low intensity because the orbitals involved are perpendicular.b) Electronic transitions occur when incoming photons have energy that matches the energy gap

between the orbitals involved.

c) Absorption of UV or visible light generates a molecule in its excited electronic state.d) More conjugated systems have shortermax values than less conjugated systems.

e) HOMO LUMO transitions are of the lowest energy relative to other electronic transitions inthe same molecule.

11. (4 pts) What is the most likely product of the following reaction?

KMnO4

H3O+

HO

O

O

H

O

O

HO

O

O

HO

O

O

OHH

O

O

a) b)

c)

d) e)

12. (4 pts) Which set of reagents (in the correct order) would accomplish the following transformation?

HCH3CH2CH2

CH3

H

CH3CH2CH2

H

I II

I II

a)NaNH2/NH3(l); CH3I, H2/Lindlar catalystb) KOH/THF; CH3I H2/Pd/C

c) H2/Lindlar catalyst NaNH2/THF; CH3I

d) BH3-THF; H2O2/NaOH H2SO4e)NaNH2/THF; CH3CH2I H2/Lindlar


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13. (4 pts) A reaction of propyne with Hg2+ is run in methanol (CH3OH) in the absence of water, but inthe presence of a strong acid (H+) with a non-nucleophilic counterion. If this reaction follows a

typical mechanism of electrophilic addition, what would be the expected product?

OCH3

OCH3

CH3O OCH3

O

OCH3OCH3

O

OCH3

OCH3

a) b) c) d) e)

14. (4 pts.) Which of the following reactions would not yield at least one ketone?

a) ozonolysis (followed by reductive workup with Zn/H+) of mono-substituted alkene

b) oxidative cleavage of a trisubstituted cyclic alkene

c) oxymercuration/demercuration of terminal alkyne

d) hydroboration of an internal alkyne, followed by H2O2/NaOHe) periodate oxidation of a tertiary 1,2-diol

15. (4 pts) If the molecule shown below is treated with ozone followed by zinc and acetic acid, what arethe products formed?

O OO

H H

O O

H H

O

H

CO2

O O

O

H H

O O

O

O

H

H

CO2

O O O

HH

OO

O O

HH

O

O O

H

H

O

O O

O

H

H

b)

c)

d)

e)

a)

O O

H H

O

H

O

H

O

H

O O O

HH


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16. (4 pts) In the vinyl cation the positively-charged carbon is sp hybridized. Which statement about thehybridization typeof the negatively-charged carbon in the vinyl carbanion is correct?

a) The carbon is sp hybridized to help to stabilize the orbital with the lone pair.b) The carbon is sp hybridized to minimize repulsion between the bonding and nonbonding

electrons.

c) The carbon is sp2 hybridized to maximize scharacter in the orbital with the lone pair.d) The carbon is sp2 hybridized to minimize angle strain around the bond.

e) The carbon is sp3 hybridized to maximize separation between all electrons.f) The carbon is sp3 hybridized to avoid antiaromaticity that would be present if it were planar.

17. (4 pts) Which of the molecules listed below can be synthesized from propyne using only oneof thereactions discussed in Chem 210? Using a reagent in excess is considered as a one-step reaction.

BrBrBr

Br

BrBrO

H

O

A B C D

a) A and B b) C and D c) A, B,and D d) B, C, and D e) all

18-19. Radicals listed below are allowed to abstract hydrogen atoms from propane.

a) Cl b) H3C c) H d) HO e) H3CS

18. (2 pts) Which radical will generate the largest ratio of 2-propyl to 1-propyl radicals?19. (2 pts) Which radical will be least selective?

20-21. Fluorocyclohexane undergoes free-radical fluorination with F2. Consider onlyproducts containing two fluorine atoms.

20. (2 pts) How many constitutional isomers with two fluorines are present?

a) 1 b) 2 c) 3 d) 4 e) 5 f) 6

21. (2 pts) How many mesocompounds with two fluorines are present?

a) 1 b) 2 c) 3 d) 4 e) 5 f) 6


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22-25. Some of the possible products of electrophilic addition of HCl to 1-phenyl-1,3-butadiene are shown below (Z-isomers have been omitted).

HCl

Cl

Cl

Cl

Cl

Cl

Cl

A B C

D E F 22. (2 pts) Which of the above chlorides is not likely to form at all?

a) A b) B c) C d) D e) E f) F

23. (2 pts) Which of the above chlorides is expected to be the major product under

thermodynamic control?


24. (2 pts) Which products are 1,4 adducts?

a) A and F b) B and E c) B and F d) C and F e) D and E

25. (2 pts) Which 1,2-adduct would be produced in the largest quantities underthermodynamic control?


26. (4 pts) Which of the following is not the product of a radical chain-reactionof 2-pentene with NBS?

Br

Br

Br

Br

a) b) c) d)


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27. (4 pts) Which is the most likely protonation site in the conjugated alkene shownbelow?

1

23

45

a) 1 b) 2 c) 3 d) 4 e) 5

28- 30For questions 28-30consider the retrosyntheticanalysis for the target ketoneshown below:

28. (4 pts) Based on the reactions covered so far in Chem 210, which of thefollowing structures is not an immediate precursor to the target molecule?

a) A b) B c) C d) D e) E

29. (4 pts) Which of the following pairings of a synthetic precursor (see above)with reagents will yield the target compound?

a) A reacted with KMnO4/H+ b) B reacted with O3

c) C reacted withO3; Zn/AcOH d) D reacted with H2/Lindlar catalyste) E reacted with KMnO4/NaOH

30. (4 pts) If the starting materials are limited to building blocks containing no morethan 2 carbons, which precursor (see above) will be part of the shortest (feweststeps) synthesis?

a) A b) B c) C d) D e) E

===========================================================================

End of the exam

O

?

OOH

HO

A B C D E


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Total Strain Energies in Cycloalkanes

ring size kJ/mol kcal/mol

3 115 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 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 2.6

CH3-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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Answer key: 3C

1. E2. C3. C4. C (2 pts)

5. E (2 pts)6. A7. B8. D9. D10.D11.A12.A13.C14.A15.E16.C

17.E18.E (2 pts)19.D (2 pts)20.D (2 pts)21.B (2 pts)22.D (2 pts)23.F (2 pts)24.B (2 pts)25.F (2 pts)26.B27.A28.A

29.C30.B

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Practice 3C