final exam practice-3b

Chem 210 Practice Exam 3B

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Organic Chemistry: Chem 210

Practice Exam 3B

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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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 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 - 2. Radicals can be compared according to their selectivity in hydrogen abstraction reactions based on the

reactivity-selectivity principle. Compare the following carbon-centered radicals: a) HCC b) H3C c) Ph d) NC e) H2C=CHCH2

1. (4 pts) Which of the above radicals would be expected to be the most selective? 2. (4 pts) Which of the above radicals would be expected to be the least selective?

3. (4 pts) Which of the following MO energy diagrams corresponds to the cyclobutadienyl dication?

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

a) 1 b) 2 c) 3 d) 4 e) 8

a) b) c) d) e)

H2

Pd/C



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5. (4 pts) The following transformation is carried out in three steps (I - III). What are the appropriate reagents for the first (I) step?

a) Br2/H2O e) HgSO4/H2SO4/H2O b) NaNH2/THF f) BH3THF; H2O2/NaOH c) NBS/CCl4 g) Hg(OAc)2/H2O; NaBH4 d) Br2/CCl4 h) KMnO4/NaOH

6. (4 pts) Which of the compounds listed below is a product of the following reaction?

7. (4 pts) (R)-2-fluorobutane undergoes free-radical fluorination with F2. Including stereoisomers, how

many products containing two fluorine atoms will form in this reaction?

a) 3 b) 4 c) 5 d) 6 e) 7 f) 8 8. (4 pts) Which of the following molecules are aromatic?

A B C

D E

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

O

I II III

CH3NBS

DMSO, H2O

CH3

HOH

Br

OH

HCH3

Br

CH3

BrBr

H

Br

HCH3

OH

CH3

HOH

OH

Br

OHCH3

H

a) b) c)

d) e) f)



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9-11. For questions 9 - 11 consider the retrosynthetic analysis for the target aldehyde shown below:

9. (4 pts) Based on the reactions covered in Chem 210, which of the following structures is not an

immediate precursor to the target molecule?

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

10. (2 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 Hg(OAc)2/H2O; NaBH4 c) C reacted with HIO4/THF/H2O d) D reacted with HgSO4/H2SO4/H2O e) E reacted with KMnO4/H+ f) E reacted with Hg(OAc)2/H2O; NaBH4

11. (4 pts) If the starting materials are limited to acetylene (HCCH) and compounds containing only one carbon, which precursor (see above) will be the part of the shortest (fewest steps) synthesis?

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

12. (4 pts) Consider the following reaction of 1-methylcyclohexene with NBS. Four likely products of this

reaction are shown below. One of the likely products is not shown, however.

Which of the following is the "missing" product of that reaction?

O

H?

OH

OH

H

A B C D E

NBS

CCl4

Br

Br

Br

Br+ + + + ?

Br Br Br

Br BrBr

a) b) c) d) e)



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13. (4 pts) When reacted with an alkene, which of the following reagents would not introduce at least one OH group into the final product?

a) Hg(OAc)2/H2O; NaBH4 b) BH3THF; H2O2/NaOH c) OsO4; NaHSO3 d) KMnO4/NaOH e) HIO4/H2O/THF f) NBS/H2O/DMSO

14. (4 pts) A schematic representation of -type molecular orbitals for 3-methylene-1,4-pentadiene is shown

below. The orbitals are arranged in random order. Which of the following electronic transitions will correspond to the absorption band with the shortest wavelength?

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

15. (4 pts) Which starting material should be used to produce the compound shown below?

16. (4 pts) What is the best way to carry out the following transformation?

H O

H

a) KMnO4/ H3O+ b) HgSO4/H2SO4/H2O c) H2/Lindlar; O3; Zn/H3O+ d) BH3; NaOH/H2O2 e) Hg(OAc)2/H2O; NaBH4 f) HIO4/H2O

A B C

D E F

? 1. O32. Zn/AcOHO

O

H O

H

O

a) b) c)

d) e)



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17. (4 pts) Which is the least likely protonation site in the conjugated alkene shown below?

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

18. (4 pts) Compound X shows a single UV absorption at 226 nm, and it can be catalytically hydrogenated to

yield 2,6-dimethyloctane. On ozonolysis followed by treatment with zinc and acetic acid, compound X yields formaldehyde (H2CO), acetone ((CH3)2CO), and the dialdehyde shown below. What is the structure of compound X?

19. (4 pts) Which of the following statements best explains why 1-propyne can be deprotonated by the ethyl

anion (CH3CH2)?

a) the acetylide anion is a stronger base than the ethyl anion b) ethane has a lower pKa than acetylene c) the lone-pair orbitals in acetylide anions have more s character than those in alkyl anions d) the acetylide anion is a weaker base than an alkyl anion e) the lone-pair orbitals in acetylide anions have more p character than those in alkyl anions

20. (4 pts) What is the most likely product of the following reaction?

12

34

5 6

HCCH2CH2C

O O

CH

O

(dialdehyde)

a) b)

c) d)

e)

CHCH3H2SO4

CH2CH3

OH

CH2CH3 CH2CH2OHOH

OH

a) b) c) d) OH

H2O

e)



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21. (4 pts) Which of the following mechanisms is the most likely reaction path for the transformation shown below?

a)

b)

c)

d)

HBr-Br

BrH

OH H

-H O H

Br H OBr

H OBrBr2

H2O

HOH2

OHH

Br

-HBr

OHH

OBr

H

Br--Br

Br

H

OH

Br

H-HO

Br

OH H

HH2OBr

OHH

Br-H

OH

Br

Br

Br

OBr

Br Br



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22. (4 pts) Assuming that only monochlorides are products in the reaction shown below, what would be the expected ratio of the two alkyl chlorides formed in that reaction?

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

23. (4 pts) Which of the sets of reagents shown below would accomplish the following transformation?

A B a) BH3THF; H2O2/NaOH H2SO4 b) H2/Pd/C BH3THF; H2O2/NaOH c) H3PO4 Hg(OAc)2/H2O; NaBH4 d) KOH Hg(OAc)2/H2O; NaBH4 e) NaOH BH3THF; H2O2/NaOH

24 - 25. Consider the following electrophilic addition of HCl to 2-methyl-1,3-cyclohexadiene.

24. (2 pts) Which of the above chlorides is not going to form in this reaction?

a) A b) B c) C d) D e) all of them (A-D) are products of the addition

25. (2 pts) Which of the above chlorides is expected to be the major product under the conditions

specified?

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

1 eq HCl

ether, low temperature

ClCl

Cl Cl

A B C D

Br 1. A2. B OH

Cl2hv



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26 - 28. Iodine azide, IN3, adds to 1-methylcyclohexene by an ionic two-step mechanism similar to those discussed in our class for other electrophiles. Only the products shown below form in that reaction.

26. (2 pts) What is the first intermediate formed in that reaction?

a) a teriary carbocation b) iodonium ion c) azidonium ion d) an allylic carbocation

27. (2 pts) What is the stereochemistry of the addition?

a) syn b) anti c) syn/anti (50:50) d) cannot be determined

28. (2 pts) What is the nucleophile in the second step?

a) N3 b) I c) H d) iodonium ion

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

End of the exam

CH3 IN3 N3

H

CH3

IH

CH3

I

N3

+



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Total Strain Energies in Cycloalkanesring 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 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: 3 B

1. E 2. D 3. B 4. A 5. D 6. B 7. C 8. D 9. B 10. C 11. D 12. E 13. E 14. D 15. B 16. C 17. A 18. C 19. C 20. A 21. A 22. E 23. D 24. B 25. A 26. B 27. B 28. A

final exam practice-3b

Documents

practice exam

exam results

pencil exam policy

relative stereochemistry

unspecified stereochemistry

stereochemistry conventions

test form white

answer key