Practice Questions for Exam 2 Use these practice questions ...

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Practice Questions for Exam 2

CH2230 Fall 2018

Clemson University

1. How many carbon chiral centers are present in the

structure of Gentiopicroside, an anticonvulsant

agent?

A. 4 D. 7

B. 5 E. 8

C. 6

2. For the circled carbon in the Fischer projection of

D-glucose, what are the Cahn-Ingold-Prelog

priorities for the groups pointing up and down?

A. Up: 1, Down: 2 C. Up: 2, Down: 3

B. Up: 2, Down: 1 D. Up: 3, Down: 2

E. None of the above

3. Which of the following can exist as a meso isomer?

A. I

B. II

C. III

D. IV

4. Which of the following molecules is an enantiomer

for (1R,2S)-1-bromo-2-isopropyl cyclohexane?

5. What is the relationship between the molecules

represented by these two structures?

A. Enantiomers

B. Diastereomers

C. Constitutional isomers

D. Configurational Isomers

E. Identical

6. What is the relationship between the molecules

represented by these two structures?

A. Enantiomers

B. Diastereomers

C. Constitutional isomers

D. Sisters

E. Identical

7. Which of the following choices is a diastereomer of

the first structure shown?

A. I

B. II

C. III

D. IV

8. Consider these two pairs of stereoisomers. Which

pair can be separated by physical means, and

which pair would rotate plane polarized light

(PPL) in opposite directions of equal angles?

Use these practice questions to help in your preparation for the exam. Do not memorize these questions as the questions on your exam will be different.

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Physical separation Equal/opposite

rotations of PPL

A. Pair 1 Pair 2

B. Pair 2 Pair 1

C. both neither

D. neither both

9. (S)-methyl-grandfantasticoate, isolated from the

hippocampus, has a boiling point (bp) of 732 °C

and has a specific rotation of +17°. Which will be

definitely true of the as-yet undiscovered (R)-

methyl-grandfantasticoate? Side Note: A

hippocampus is not a college for hippopotamuses,

it is a part of the brain.

A. It is dextrorotatory, but we cannot predict the

bp

B. It is levorotatory, but we cannot predict the bp

C. It has a specific rotation of 17° and bp = –732

°C

D. It has a specific rotation of –17° and bp = 732

°C

E. None of these is definitely true

10. Ethylbromide reacts with sodium acetate. What is

the mechanism and what is the major product?

11. Which of the following four molecules is different

from the others?

A.

B.

C. (R)-2-butanol

D.

12. Which of the following structures is the Fischer

projection for the given wedge-dash structure?

13. Which of molecules below is/are the same

stereoisomer as this one?

A. 1 and 2

B. 1 and 3

C. 2 and 3

D. only 2

E. only 3

14. Which Fischer projection represents the same

molecule as that represented by the line-bond

structure below? Note: iPr stands for isopropyl.

E. None of these

15. Which of the following is a correct Fischer

projection of the following compound?

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A. I B. II

C. III D. IV

16. Which of the following energy diagrams shows a

concerted exergonic (thermodynamically favorable)

reaction?

17. Which of the following energy diagrams is of a

reaction with two transition states and one

intermediate?

18. Which of the following cannot be a nucleophile?

A. I B. II

C. III D. IV

19. Which atom has 1 lone pair of electrons?

Which has 2 lone pairs of electrons?

Which has 0 lone pairs of electrons?

20. In each pair given, which carbocation is more

stable?

A. I and III

B. I and IV

C. II and III

D. II and IV

21. Which labeled hydrogen in the

dehydrobromination of the following molecule in

presence of KOH (E2 conditions) will make the

most thermodynamically stable product?

A. H1 B. H2

C. H3 D. H4

22. Which of the following reaction coordinate

diagrams represents the fastest forward reaction?

23. Which of the following reaction coordinate

diagrams is the only one that can represent a

reaction that occurs via a carbocation?

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24. Write out the mechanism for the SN2 reaction of 1-

bromo-2-methylbutane with sodium ethoxide

(NaOEt) to help you choose which statement is

most correct.

A. The first mechanistic step is slow and produces

a carbocation which rearranges before the fast

nucleophilic attack step. The product is an

ether.

B. The first mechanistic step is slow and produces

a carbocation which rearranges before the fast

nucleophilic attack step. The product is an

ester.

C. The ethoxide nucleophile attacks at the same

time the bromide leaves. The product is an

ether.

D. The ethoxide nucleophile attacks at the same

time the bromide leaves. The product is an

ester.

25. Which of the following is the least reasonable

carbocation rearrangement?

A.

B.

C.

D.

26. What is a viable substitution product for the

following SN1 reaction?

A. I B. II

C. Both II & III D. Both IV & V

27. Which of the following is a strongest nucleophile

in a polar protic solvent?

A. F-

B. Cl-

C. Br-

D. I-

E. All of these

28. What would be the major elimination (E1) product

of this reaction?

29. Which describes the major product for the reaction

shown?

A. A sulfonate ester in the R-configuration

B. A sulfonate ester in the S-configuration

C. A monosubstituted alkene

D. A trisubstituted alkene

E. A tetrasubstituted alkene

30. Which of the following reactions is predicted to be

the fastest in SN2 mechanism?

A. Reaction of 1-bromobutane with NaI in DMSO

B. Reaction of 2-bromobutane with NaOEt in

EtOH

C. Reaction of methylbromide with NaI in DMSO

D. Reaction of 1-bromobutane with NaOEt in

EtOH

A B

C D

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E. All of them have same rate

31. Consider these solvents. Which are polar protic,

and which are polar aprotic?

Hexane, C6H14

Dichloromethane, CH2Cl2

Acetone, CH3COCH3

Water, H2O

Methanol, CH3OH

Polar protic polar aprotic

A. H2O, CH3OH CH2Cl2, CH3COCH3

B. all none

C. none all

D. H2O, CH3COCH3 CH3OH, C6H14,

E. CH2Cl2, CH3COCH3 H2O, CH3OH

32. What is the maximum number of possible

stereoisomers for this molecule?

33. Which reagent produces the greatest amount of

non-Zaitsev (Hofmann) product upon reaction with

(R)-2-bromobutane?

A. LiNH2

B. NaOEt

C. KOC(CH3)3

D. KOC(O)CH3

E. KOCH3

34. When 1-iodo-2-methylpentane undergoes an E1

reaction with water and heat, what is the major

product?

A. 2-methyl-2-pentanol

B. 2-methyl-1-pentene

C. 4-methyl-2-pentene

D. 2-methyl-2-pentene

E. 2-methyl-3-pentanol

35. Which of the following alkyl halides will give the

following product as a major product?

A. only I D. I and II

B. only II E. II and III

C. only III

36. Which one of these reaction conditions will yield

exclusively one of the reaction types discussed in

Chapter 7?

A. (R)-2-bromobutane and sodium tert-butoxide

B. (R)-2-bromobutane and sodium methoxide

C. (R)-2-bromobutane, methanol, and heat

D. Bromomethane and sodium tert-butoxide

E. Iso-propyl bromide and sodium methoxide

37. Which cyclohexyl bromide is expected to undergo

the most facile E2 elimination?

38. Which of the following is correct about the

substitution reaction of (2R,4R)-2-chloro-4-

methylheptane with sodium methoxide?

A. A (2R,4R) product will primarily form

B. A (2R,4S) product will primarily form

C. A (2S,4R) product will primarily form

D. The 2 position will racemize

E. The 4 position will racemize

39. Except in organic chemistry textbooks, SN1 and

SN2 reactions rarely compete because:

A. The degree of substitution required to stabilize

SN1 carbocations usually sterically hinders SN2

B. The formation of carbocations is usually

significantly energetically unfavored even for

secondary carbons

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C. Both temperatures and especially solvents that

support either SN1 or SN2 generally disfavor

the other

D. Any practicing chemist doesn’t randomly

choose reaction conditions, and researching

literature conditions will generally preclude

any textbook hypothetical scenarios where

both SN1 and SN2 compete

E. One does have to be slightly careful about

benzylic positions, especially adjacent to

electron rich aromatics

F. All of the above are true

40. Question deleted so you can rest.

41. Which best describes the species resulting from a

thermodynamically-favorable carbocation

rearrangement of the cation shown?

Note: Symbol D indicates deuterium, an isotope of H

with atomic mass of 2 amu.

A. There is a chiral center in the S-configuration

B. There is a chiral center in the R-configuration

C. It will be a racemic mixture

D. It has two chiral centers

E. It is achiral

42. Which of the following best describes the

statement “3° carbocations are more stable than 2°

carbocations” for identifying the major product of

this reaction?

A. True and very relevant

B. False but very relevant if true

C. True and minimally relevant

D. False and minimally relevant




this reaction?








this reaction?





45. Consider this reaction and the corresponding

reaction coordinate diagram:

Which best describes the organic species at point “I”

on this reaction coordinate diagram?




this reaction?




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47. Which reaction mechanism is second order,

concerted, speeds up if the base concentration is

increased, is indifferent to carbocation

intermediates or their rearrangements but might

require careful consideration of a Newman

Projection or a 1,2-trans (diaxial) chair

cyclohexane conformation, has one transition state

in which two sigma bonds break, one sigma bond

forms, and a pi bond forms, and makes a product

of the general formula CnH2n?

A. SN1

B. SN2

C. E1

D. E2

E. None or more than one of these.

The next six (6) questions refer to this reaction.

48. Which mechanism produced the indicated product?

A. E2

B. E1

C. SN2

D. SN1

49. The rate law is ___ and the reaction coordinate

diagram has __ humps (energy barriers).

A. 1st order / 1

B. 1st order / 2

C. 2nd order / 1

D. 2nd order / 2

50. Which is the transition state for the slow step?

A. C.

B. D.

51. If [Nuc−] is tripled, the reaction rate will…

A. triple

B. double

C. not change

D. reduce by a factor of 1/3

52. If the leaving group is changed to fluorine…

A. the overall reaction rate should increase.

B. the overall reaction rate should decrease.

C. the overall reaction rate should remain the

same. D. the rate of the slow step will decrease but

increase the rate of the fast step giving an

overall faster reaction.

53. Depending on reaction conditions (like choice of

solvent, and basicity of the nucleophile), which of

these are possible minor products?

A.

B.

C. D. Only 2 of these.

E. All 3 of these.

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______________________________________________________________________________________________ USEFUL INFORMATION: _______________________________________________________________________________________

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Question number Answer

1 D

2 C

3 A

4 C

5 E

6 B

7 B

8 A

9 D

10

SN2,

11 D

12 B

13 B

14 A

15 A

16 C

17 B

18 A

19 1 LP A

2 LP D and E

0 LP B and C

20 A

21 A

22 B

23 C

24 C

25 A

26 B

27 D

28 A

29 A

30 C

31 A

32 2

33 C

34 D

35 A

36 D

37 D

38 C

39 F

40 zzz

41 C

42 C

43 C

44 C

45 D

46 D

47 D

48 D

49 B

50 C

51 C

52 B

53 D

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