Deck 5: Stereochemistry

Question 1

What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,4R)-2,3,4-trichloroheptane?

A) not isomers
B) constitutional isomers
C) enantiomers
D) diastereomers
E) conformers

Answer 1

enantiomers

Question 2

________ are isomers which have the same bonding sequence but differ in the orientation of their atoms in space.

Answer 2

Stereoisomers

Question 3

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Answer 3

enantiomers

Question 4

How many asymmetric carbons are present in the compound below?

Question 5

What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,5R)-2,3,5-trichloroheptane?

A) not isomers
B) constitutional isomers
C) enantiomers
D) diastereomers
E) conformers

Question 6

Star the asymmetric carbons in the structure below.

Question 7

How many asymmetric carbons are present in the compound below?

Question 8

How many asymmetric carbon atoms are present in the molecule shown?

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

Question 9

What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

A) not isomers
B) constitutional isomers
C) enantiomers
D) diastereomers
E) conformers

Question 10

How many asymmetric carbon atoms are present in the molecule shown?

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

Question 11

How many asymmetric carbons are present in the compound below?

Question 12

Does this molecule have a mirror plane? If so, represent where the plane would be with a dashed line.

Question 13

How many asymmetric carbon atoms are present in the following compound?

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

Question 14

Is the molecule shown below chiral or achiral?
(CH₃)₃CCH(CH₃)₂

Question 15

Which of the following incorrectly describes cis-1,2-dimethylcyclopentane?

A) It is a meso compound.
B) It is achiral.
C) It contains two asymmetric carbons.
D) Its diastereomer is trans-1,2-dimethylcyclopentane.
E) It has an enantiomer.

Question 16

How many enantiomers are there of the molecule shown below?

A) 0
B) 1
C) 2
D) 3
E) 6

Question 17

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Question 18

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Question 19

How many asymmetric carbon atoms are present in the following compound?

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

Question 20

What is the structural relationship between the two molecule shown below?

A) constitutional isomers
B) enantiomers
C) diastereomers
D) conformational isomers
E) not isomers

Question 21

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Question 22

If possible, draw the structure of the enantiomer of the molecule shown below.

Question 23

How many asymmetric carbons are present in the compound below?
3-ethyl-2,2,4-trimethylpentane

Question 24

Consider the four substituents below. Order them in decreasing priority according to the Cahn-Ingold-Prelog priority system. (Highest priority is first, lowest is last.)
-CH
CH₂, -C(CH₃)₃, -CH₂OH, -COOH

Question 25

Circle all structures shown below that are chiral.

Question 26

Is the molecule shown below chiral or achiral?

Question 27

Circle each chiral molecule among those shown below.

Question 28

Is the mirror image of the following molecule an enantiomer or is it superimposable with it?

Question 29

Is the molecule shown below chiral or achiral?

Question 30

Is the molecule shown below chiral or achiral?

Question 31

Is the molecule shown below chiral or achiral?
CH₃CH₂CH(CH₃)CH₂CH₃

Question 32

Draw the enantiomer of the molecule shown below.

Question 33

Which of the statements below correctly describes an achiral molecule?

A) The molecule has a nonsuperimposable mirror image.
B) The molecule exhibits optical activity when it interacts with plane-polarized light.
C) The molecule has an enantiomer.
D) The molecule might be a meso form.
E) None of the above

Question 34

Star the chirality centers in the molecule below.

Question 35

Circle each chiral molecule among those shown below.

Question 36

Is the molecule shown below chiral or achiral?

Question 37

Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

Question 38

Consider the four substituents below. Order them in decreasing priority according to the Cahn-Ingold-Prelog priority system. (Highest priority is first, lowest is last.)
-D, -H, -CH₃, -CH₂CH₃

Question 39

How many asymmetric carbons are present in the compound below?

Question 40

Is the molecule shown below chiral or achiral?

Question 41

Label each asymmetric carbon in the compound below as R or S.

Question 42

Label each asymmetric carbon in the compound below as R or S.

Question 43

Draw the structure of (S)-1-bromo-1-chloropropane. Take particular care to indicate three-dimensional stereochemical detail properly.

Question 44

Assign the proper configurational label, R or S, to each chiral carbon in the molecule below.

Question 45

Draw the structure of (2R,3R)-2,3-dibromo-3-chloropentane.

Question 46

Label each asymmetric carbon in the compound below as R or S.

Question 47

Draw the structure of any diastereomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Question 48

Draw the structure of (2R,3S)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Question 49

Which of the following structures are achiral and meso?

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

Question 50

How many asymmetric carbons are present in the compound below?

Question 51

Draw the structure of (1R, 2R)-1-bromo-2-chlorocyclobutane. Take particular care to indicate stereochemistry properly.

Question 52

Draw the structure of (1R, 2S, 3S)-1,2-dibromo-3-ethylcyclohexane. Take particular care to indicate stereochemistry properly.

Question 53

Draw the Fischer projection of (S)-2-bromobutane.

Question 54

Draw the structure of the enantiomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Question 55

Label each asymmetric carbon in the molecule below as having the R or S configuration.

Question 56

Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.

Question 57

Label each asymmetric carbon in the compound below as R or S.

Question 58

Draw the structure of (S)-3-chloro-3-methylhexane. Take particular care to indicate stereochemistry properly.

Question 59

Label each asymmetric carbon in the compound below as R or S.

Question 60

Does the molecule shown below contain asymmetric carbon atoms? Is this molecule chiral?

Question 61

Which of the following statements is (are) true for the compound (R)-2-butanol?

A) This compound is chiral.
B) This compound is optically active.
C) This compound has an enantiomer.
D) all of the above
E) none of the above

Question 62

Captopril is used to treat high blood pressure and congestive heart failure. Label the chiral centers as R or S.

Question 63

Label each asymmetric carbon in the compound below as R or S.

Question 64

Predict the specific rotation of the compound shown.

A) It is impossible to predict; it must be determined experimentally.
B) Because both asymmetric centers are R, the compound is dextrorotatory.
C) Because both asymmetric centers are S, the compound is levorotatory.
D) Zero; the compound is achiral.
E) Because this compound represents a racemic mixture, the compound is dextrorotatory.

Question 65

If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture?

A) 100
B) 75
C) 50
D) 25
E) 3

Question 66

Glucose has a specific rotation of +52.8°. Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8° was observed.

A) 0.299 g/mL
B) 0299 g/mL
C) 3.34 g/mL
D) 334 g/mL

Question 67

Which of the following statements correctly pertains to a pair of enantiomers?

A) They rotate the plane of polarized light by exactly the same amount and in opposite directions.
B) They rotate the plane of polarized light by differing amounts and in opposite directions.
C) They rotate the plane of polarized light by differing amounts and in the same direction.
D) The have different melting points.
E) They have the same melting point, but they have different boiling points.

Question 68

If (S)-glyceraldehyde has a specific rotation of -8.7°, what is the specific rotation of (R)-glyceraldehyde?

A) 0.0°
B) -8.7°
C) +8.7°
D) cannot be determined from the information given

Question 69

Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde.

Question 70

Can one predict whether a compound with a single asymmetric carbon is dextro- or levorotatory based on the R/S assignment at this asymmetric carbon? Explain briefly.

Question 71

A mixture of two enantiomers with a composition of 65.0% R has an observed rotation of -25.3° in a polarimeter tube. If the mixture has a concentration of 2.038 g/mL at 25°C, what is the predicted
Of an optically pure sample of the S enantiomer?

A) -25.3°
B) -53.5°
C) +12.4°
D) +41.3°
E) +53.5°

Question 72

Compounds that rotate the plane of polarized light clockwise are called ________.

Question 73

A mixture of equal amounts of two enantiomers ________.

A) is called a racemic mixture
B) is optically inactive
C) implies that the enantiomers are meso forms
D) both A and B
E) none of the above

Question 74

Phantasmidine, shown below, is found in poisonous frog skin and has analgesic properties (J. Nat. Prod. 2010, 331). Assign each chiral center as having either R or S configuration.

Question 75

For the structure shown below, draw the stereoisomer having a configuration of (1R,3S,4S) in a perspective structure.

Question 76

Label each asymmetric carbon in the compound below as R or S.

Question 77

A student measured the optical activity of an unknown sugar at two different concentrations. The results of his measurements are shown below. Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: Consider each measurement of plane polarized light has a true reading and a "ghost" reading 180° from the true reading).
Concentration observed rotation
2)00 g sugar in 10.0 mL water +159.1°
5)00 g sugar in 10.0 mL water +127.8°

A) -10.5°
B) +25.6°
C) +79.5°
D) -105°
E) +256°

Question 78

Which of the following configurations corresponds to the structure below?

A) (4R, 5R)
B) (4R, 5S)
C) (4S, 5R)
D) (4S, 5S)

Question 79

A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57°, what is the specific rotation of this natural product?

Question 80

Would a 50:50 mixture of (2R,3R)-2,3-dibromobutane and (2R,3S)-2,3-dibromobutane be optically active? Explain.