stereochem test bank

Chapter 5

1. Designate the following compound as R or S.

A) R B) S

Ans: B


Cl

H A) R B) S

Ans: B


Cl OH

H Br

A) R B) S

Ans: B


Br I A) R B) S

Ans: B


HO I

O

OH A) R B) S

Ans: B


I

H

A) R B) S

Ans: B


HOBr

H Br A) R B) S

Ans: A

8. Designate each of the chiral centers in the following compound as R or S.

Cl

OHH

H

Cl

Cl

a

b

A) a = S; b = S B) a = R; b = S C) a = R; b = R D) a = S; b = R

Ans: D

9. Consider the following compound. Rank the priority of the groups around the chiral

carbon. Label the highest-priority group as 1, the lowest-priority group as 4, and the

groups of intermediate priority as 2 and 3.

OH

O

Br

OH

O

BrOH

O

Br

OH

O

Br

OH

O

Br

OH

O

Br

1

23

4

1

2

3

4

1

2 3

4

1

23

4

1

2

3

4

A B C

D E A) A B) B C) C D) D E) E

Ans: B

10. Select the list that places the substituents from the highest priority to the lowest priority.

A) –CH2Br; –Br; –Cl; –CH3 C) –OCH3; -–OH; –CH3; –H

B) –CH2CH3; –CH3; –CH2OH; –H D) –CH2CH2I; –HC CH2; –CH3; –H

Ans: C

11. Select the highest-priority substituent of the following list.

CH CH2A. B. CH2 Cl C. D. OH E.CH2 OH CH2 CH3 A) A B) B C) C D) D E) E

Ans: D

12. Rank the following groups in order of increasing priority.

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

Ans: C

13. How many stereogenic centers are present in the following compound?

A) 0 B) 1 C) 2 D) 3 E) 4

Ans: D


A) 0 B) 1 C) 2 D) 3 E) 4

Ans: B


A) 0 B) 1 C) 2 D) 3 E) 4

Ans: C


A) 0 B) 1 C) 2 D) 3 E) 4

Ans: A

17. This question is based on the natural product menthol, whose structure is drawn below.

Which drawing highlights the stereocenters of menthol?

A) A B) B C) C D) D E) E

Ans: D

18. How many possible stereoisomers does menthol have?

A) 6 B) 4 C) 3 D) 5 E) 8

Ans: E

19. How many stereocenters are present in 2,6-dimethyloctane?

A) 0 B) 1 C) 2

Ans: B

20. How many stereocenters are present in 1,3-dimethylcyclopentane?

A) 0 B) 1 C) 2

Ans: C

21. How many stereocenters are present in 3,4,5,6-tetraethyldecane?

A) 2 B) 3 C) 4

Ans: B

22. Which drawing highlights all of the stereocenters in heroin, shown below?

O

CH3COO

HN

CH3

CH3COO

heroinaddicting drug

O

CH3COO

HN

CH3

CH3COO

H

H

A.

O

CH3COO

HN

CH3

CH3COO

H

B.

O

CH3COO

HN

CH3

CH3COO

H

C.

O

CH3COO

HN

CH3

CH3COO

H

D.

O

CH3COO

HN

CH3

CH3COO

H

E. A) A B) B C) C D) D E) E

Ans: A

23. How many stereocenters are present in taxol, shown below?

A) 8 B) 9 C) 10 D) 11 E) 12

Ans: D

24. Which drawing indicates the stereocenters in cholesterol, shown below?


Ans: C

25. How many stereocenters are in the compound below?

A) 3 B) 4 C) 5 D) 6 E) 8

Ans: B

26. How many stereocenters are present in the following compound?

OH

O OH

O

HO

H A) 2 B) 3 C) 4 D) 5 E) 6

Ans: C

27. Which of the following compounds is (are) chiral?

Cl

Cl

H

Cl

A

H3C

CH3

Cl H

H Cl

B A) A B) B C) A and B

Ans: A

28. Which of the following drawings represents the enantiomer of compound X?

OH

OH

OH

OH

OH

OH

OH

OH

A B C

X

A) A B) B C) C

Ans: B

29. What is the percent ee of a mixture that has 80% of one enantiomer and 20% of the

other?

A) 80 B) 120 C) 60 D) 90

Ans: C

30. If a mixture has an ee of 70%, what is the percentage of each enantiomer?

A) 75% : 25% B) 85% : 15% C) 95% : 5% D) 90% : 10%

Ans: B

31. A reaction mixture is three parts of one enantiomer and one part of the other. What is

the percent ee of this mixture?

A) 75 B) 40 C) 65 D) 50

Ans: D

32. If a mixture has an ee of 40%, what is the percentage of each enantiomer?

A) 70% : 30% B) 60% : 40% C) 80% : 20% D) 75% : 25%

Ans: A

33. Which of the following statements is (are) true about cis- and

trans-1,3-dimethylcyclohexane?

A) The cis isomer is more stable than the trans isomer because both CH3 groups can

occupy the more roomy equatorial position.

B) The trans isomer is more stable than the cis isomer because the two CH3 groups

are further away from each other.

C) The cis isomer is achiral, but the trans isomer exists as two enantiomers.

D) Statements (The cis isomer is more stable than the trans isomer because both CH3

groups occupy the more roomy equatorial position) and (The cis isomer is achiral,

but the trans isomer exists as two enantiomers) are both true.

E) Statements (The trans isomer is more stable than the cis isomer because the two

CH3 groups are further away from each other) and (The cis isomer is achiral, but

the trans isomer exists as two enantiomers) are both true.

Ans: D

34. Consider compounds A and B drawn below. Which of the following statements is

true?

H Cl

H Cl

A B

H

Cl

Cl

H

A) A and B are enantiomers.

B) A and B are diastereomers.

C) A and B are constitutional isomers.

D) A and B are two conformers of the same molecule.

E) A and B are not isomers.

Ans: B

35. Which of the following statements is (are) true about compounds A–D drawn below?

H

CH3

HO

H

A B C D

HO CH3O

HH

H H O

A) A and B are constitutional isomers. D) C is optically active.

B) B and C are constitutional isomers. E) All of the choices are true

statements.

C) D is a constitutional isomer of B.

Ans: B

36. Which of the following is the enantiomer of the given compound?

H

Br

Cl

H

H

H

Cl

Br

H

Cl H

Br

H

Cl

Br

H Cl

H

Br

H

A B C D A) A B) B C) C D) D

Ans: C

37. Which of the following statements is true about compounds a and b drawn below?

A) a and b cannot be separated by fractional distillation using an efficient

fractionating column.

B) a and b rotate the direction of plane-polarized light to an equal amount, but in

opposite directions.

C) a and b are enantiomers.

D) a and b are both chiral compounds.

E) A mixture of a and b will show optical activity.

Ans: E

38. Which of the following statements is (are) true about compounds A and B drawn below?

H

OHH

HO

OH

OH

A B A) A and B have different physical properties.

B) A mixture of A and B will show no optical activity.

C) A and B are both chiral.

D) Statements (A and B have different physical properties) and (A mixture of A and

B will show no optical activity) are true.

E) Statements (A and B have different physical properties) and (A and B are both

chiral) are true.

Ans: E

39. Considering molecules A and B drawn below, which of the following statements is true?

A) A and B are constitutional isomers.

B) A and B are enantiomers.

C) A and B are diastereomers.

D) A and B are two representations of the same compound.

E) A and B are both meso compounds.

Ans: B

40. Which of the following statements is (are) true about A, B, and C drawn below?

A) A and B are enantiomers of each other.

B) B and C are diastereomers of each other.

C) An equal mixture of A and B is optically active.

D) An equal mixture of B and C is optically active.

E) Both (B and C are diastereomers of each other) and (An equal mixture of A and B

is optically active) are true statements.

Ans: C

41. Why is trans-1,2-dimethylcyclohexane more stable than cis-1,2-dimethylcyclohexane?

A) The trans isomer has one axial and one equatorial methyl group.

B) The trans isomer has two equatorial groups.

C) The trans isomer has the two CH3 groups further away from each other.

D) The trans isomer has two CH3 groups in an anti-arrangement.

Ans: B

42. How are compounds A and B related?

H Cl

H Cl

H

Cl

Cl

Cl

H

H

A B

H Cl

A) A and B are enantiomers.

B) A and B are diastereomers.

C) A and B are constitutional isomers.

D) A and B are two representations of the same compound.

E) A and B are not isomers of each other.

Ans: D

43. How are compounds b and d related to each other?

A) They are enantiomers.

B) They are diastereomers.

C) They are constitutional isomers.

D) They are two representations of the same compound.

E) They are not isomers of each other.

Ans: C

44. How are compounds d and e related to each other?






Ans: A

45. How are compounds c and e related to each other?






Ans: B

46. How are compounds a and f related to each other?






Ans: C

47. How are compounds f and g related to each other?


B) They are constitutional isomers.

C) They are two representations of the same compound.

D) They are cis-trans isomers.

Ans: D

48. How are the following two molecules related to each other?






Ans: C

49. How are the following two molecules related to each other?






Ans: D

50. Which of the following compounds is (are) chiral?

A) A B) B C) C D) D E) A and B F) B and D

Ans: F

51. An equal mixture of compounds B and C is:

A) optically active. B) optically inactive. C) You can't tell.

Ans: A

52. An equal mixture of compounds B and D is:

A) optically active. B) optically inactive. C) You can't tell.

Ans: B

53. If a mixture having all four compounds were distilled, how many different fractions

would be obtained?

A) 1 B) 2 C) 3 D) 4

Ans: C

54. R-2-pentanol and S-2-pentanol are different with respect to their:

A) boiling point and melting point.

B) melting point.

C) direction of rotation of plane-polarized light.

D) number of degrees of rotation of plane-polarized light.

Ans: C

55. The addition of HCl to 1-butene gives:

A) R-2-chlorobutane only.

B) S-2-chlorobutane only.

C) optically active mixture of 2-chlorobutane.

D) racemic mixture of 2-chlorobutane.

Ans: D

56. Look at the following two compounds. Decide if they are chiral or achiral.

CH3

A

CH3

H

B A) Compound A is chiral and Compound B is chiral.

B) Compound A is achiral and Compound B is achiral.

C) Compound A is achiral and Compound B is chiral.

D) Compound A is chiral and Compound B is achiral.

Ans: C

57. A compound having a specific rotation of [α] = +3.8° has been isolated and purified.

This information indicates that the compound:

A) is racemic. C) is levorotatory.

B) does not rotate plane-polarized light. D) is dextrorotatory.

Ans: D

58. Of the compounds given below, only one is not chiral. The compound that is not chiral

is:

A B C D E

OH

OHO


Ans: D

Challenge Questions

59. Jasplankinolide is a marine natural product with interesting biological activity. Indicate

the number of stereoisomers possible for this compound.

HN

Br N O

O

HN O

OH

O

NH

O

Jasplankinolide A) 6 B) 12 C) 20 D) 32 E) 64

Ans: E

60. Chloroamphenicol is a potent antibiotic whose stereoconfiguration is “R, R.” Which of

the following molecules represents Chloroamphenicol?

O2N

OH HN

HOO

Cl

Cl

O2N

OH HN

HOO

Cl

Cl

O2N

OH HN

HOO

Cl

Cl

O2N

OH HN

HOO

Cl

Cl

A B C D A) A B) B C) C D) D

Ans: A

61. Substitution reactions that proceed by the SN2 mechanism yield products with inversion

of stereochemistry. Provide the IUPAC name of the expected product for the following

reaction.

Br

NaN3

A) (1R, 3R)-1-Azido-3-tertbutylcyclohexane

B) (1R, 3S)-1-Azido-3-tertbutylcyclohexane

C) (1S, 3R)-1-Azido-3-tertbutylcyclohexane

D) (1S, 3S)-1-Azido-3-tertbutylcyclohexane

Ans: B

62. Pig liver esterase (PLE) is an enzyme that is used to stereoselectively hydrolyze esters.

In the following reaction, only one enantiomer of starting material reacts with PLE.

The (1R, 2R)-1,2-cyclohexanediol product has a specific rotation of -39°, and the

reaction proceeds with a 94% ee. (i) Calculate the percent of each enantiomer present.

(ii) Calculate the specific rotation of the mixture.

O

O

O

O

PLE

OH

OH

(racemic mixture) A) (i) 94% and 6%, (ii) [a] = -33° D) (i) 97% and 3%, (ii) [a] = -241°

B) (i) 98% and 2%, (ii) [a] = -37° E) (i) 94% and 6%, (ii) [a] = -241°

C) (i) 97% and 3%, (ii) [a] = -37°

Ans: C

63. The Diels-Alder reaction shown below produces a pair of disubstituted regioisomers (A

and B). For compound A, how many sets of enantiomers exist and how many sets of

diastereomers exist?

O+

O

H ∆

O

H

O O

H

O

A (major) B (minor)

+

A) 4 enantiomers, 2 diastereomers D) 2 enantiomers, 4 diastereomers

B) 4 enantiomers, 4 diastereomers E) 4 enantiomers, 8 diastereomers

C) 8 enantiomers, 4 diastereomers

Ans: D

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