Deck 4: Stereochemistry

Question 1

Sertraline (shown below) is the active ingredient in the antidepressant Zoloft.

Pure sertraline has a specific rotation [α] of +37.9° in methanol solution. What would the observed rotation α be for a mixture of 5.75g of pure sertraline in 30.0 ml of methanol if the solution is placed in a 10.0 cm polarimeter cell?

A) 72.6°
B) 19.8°
C) 7.26°
D) 198°
E) 0.726°

Answer 1

7.26°

Question 2

The absolute configuration of trans,trans-3,4-dibromo-5-methyl-1-cyclohexene below is:

A) 3 R, 4R, 5R
B) 3S, 4S, 5S
C) 3R, 4S, 5S
D) 3 R, 4R, 5S
E) 3S, 4S, 5R

Answer 2

3 R, 4R, 5S

Question 3

Which of the following pairs of molecules are enantiomers?

A)
B)
C)
D)
E)

Answer 3

Question 4

The different odors of (R)-(-) -carvone and (S) -(+) -carvone are best explained as being due to:

A) Differences in volatility between the two compounds
B) Differences in how the two compounds interact with chiral nasal receptors
C) Differences in the origins of the compounds: the (R)-compound is from spearmint, while the (S)-compound is from caraway
D) Differences in water solubility of the two compounds
E) Differences in how the body digests the two compounds

Question 5

Which of the following phrases correctly describes a racemic mixture?

A)equal mixture of enantiomers
B)unequal mixture of enantiomers
C)equal mixture of diastereomers
D)unequal mixture of diastereomers
E)optically active

Question 6

How many stereogenic carbons are in trans-2,3-dideuterobicyclo[2.2.1]heptane?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 7

Which of the following structures is achiral?

A)
B)
C)
D)
E)

Question 8

Which of these pairs of compounds would be classified as stereoisomers?

A) cis-2-hexene and trans-2-hexene
B) cis-2-hexene and trans-3-hexene
C) cis-2-hexene and cis-3-hexene
D) cis-1,2-dimethylcyclobutane and c i s-1,3 -dimethylcyclobutane
E) 2,2 -dimethylbutane and 2,3-dimethylbutane

Question 9

Which of the following molecules is achiral?

A)trans-1,2-dimethylcyclobutane
B)cis-3,4-dimethyl-3-hexene
C)2,3-dimethylpentane
D)4-methyl-2-hexyne
E)3-methylcyclopentene

Question 10

Which of the following pairs of molecules are related as diastereomers?

A)
B)
C)
D)
E)

Question 11

Which of the following structures is chiral?

A)
B)
C)
D)
E)

Question 12

Which of the following statements is true about the rotation of plane-polarized light by chiral compounds?

A)There is a direct connection between R/S configuration and the direction of rotation.
B)A mixture of enantiomers will have a larger optical rotation than either pure enantiomer.
C)Plane-polarized light is produced by passing light through an electromagnetic field.
D)The rotation of plane-polarized light is a physical property of chiral compounds.
E)The enantiomer that rotates plane-polarized light clockwise is called levorotatory, or l.

Question 13

Which of the following statements is true about enantiomers?

A)Enantiomers must have at least one stereogenic atom.
B)An enantiomer has a nonsuperimposable mirror image.
C)Enantiomers have identical physical properties.
D)Enantiomers have identical chemical properties.
E)A mixture of two enantiomers will have the same properties as the two separate enantiomers.

Question 14

Which of the following molecules contains a stereogenic carbon properly designated as R?

A)
B)
C)
D)
E)

Question 15

Which of the following pairs of molecules are not enantiomers?

A)
B)
C)
D)
E)

Question 16

Which of the following structures is the enantiomer of the molecule shown here?

A)
B)
C)
D)
E)

Question 17

If a pure sample of molecule X has an optical rotation of +15.8 degrees, what is the optical rotation of a pure sample of the enantiomer of molecule X?

A) +15.8
B) -15.8
C) 0
D) +164.2
E) This value can only be determined experimentally.

Question 18

Which of the following molecules contains a stereogenic center properly designated as S?

A)
B)
C)
D)
E)

Question 19

Which of the following molecules could be chiral?

A)2-methylhexane
B)3-methylpentane
C)2,4,6,8-tetramethylnonane
D)2,3,4-trimethylpentane
E)3-ethyl-2-methylpentane

Question 20

Which of the following structures is chiral?

A)
B)
C)
D)
E)

Question 21

Which term best describes the relationship between the molecules shown?

A)conformational isomers
B)diastereomers
C)enantiomers
D)identical
E)structural isomers

Question 22

Which of these compounds is chiral?

A) I
B) II
C) III
D) I and II
E) I and III

Question 23

Which term best describes the relationship between the molecules shown?

A)conformational isomers
B)diastereomers
C)enantiomers
D)identical
E)structural isomers

Question 24

Which of the following pairs of molecules are related as diastereomers?

A)
B)
C)
D)
E)

Question 25

Which of the following dichlorocycloalkanes is a meso compound?

A)
B)
C)
D)
E)

Question 26

Which of the following dichlorocycloalkanes is chiral?

A)
B)
C)
D)
E)

Question 27

Assign the absolute configuration at the stereogenic center of the molecule shown here.

Question 28

Draw the enantiomer of the molecule shown here.

Question 29

Which of the following techniques could not be used to resolve a racemic mixture of organic acids?

A)React the mixture with brucine and separate the salts.
B)Crystallize the acids and manually separate the crystals.
C)React the acids with ammonia and separate the salts.
D)Elute a solution of the acids through a column containing a chiral stationary phase.
E)React the mixture using an enzyme as a catalyst.

Question 30

Which statement about diastereomers is always true?

A)A mixture containing a pair of diastereomers in equal amounts will be optically inactive.
B)If a molecule can be described as a diastereomer of another molecule, it is chiral.
C)All diastereomers are achiral.
D)Every chiral molecule has at least one diastereomer.
E)A pair of diastereomers are not mirror images of one another.

Question 31

Which term best describes the relationship between the pair of molecules shown?

A)conformational isomers
B)diastereomers
C)enantiomers
D)identical
E)structural isomers

Question 32

Which is not a stereoisomer of the molecule shown here?

A)
B)
C)
D)
E)

Question 33

How many stereoisomers exist for this compound?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 34

Assign the absolute configuration at the stereogenic center in the molecule shown here.

Question 35

Which of the following molecules is achiral and meso?

A)
B)
C)
D)
E)

Question 36

The relationship between the two molecules shown below is best described as

A) same compound
B) diastereomers
C) structural isomers
D) enantiomers
E) conformational isomers

Question 37

Which of the following is a meso compound?

A)

B)
C)
D)
E)

Question 38

Put a star next to each stereogenic carbon in the structure shown here.

Question 39

Which of the following structures is the enantiomer of the structure shown here?

A)
B)
C)
D)
E)

Question 40

What is the correct term that describes the process for separating a pair of enantiomers?

A)Racemization
B)Resolution
C)Equilibration
D)Rotation
E)Reconfiguration

Question 41

Distinguish between the terms enantiomers and diastereomers.

Question 42

Assign the absolute configuration of each stereogenic center in the natural product shown here as R or S.

Question 43

How many stereoisomers are possible for this molecule?

Question 44

Explain why butane is an achiral molecule even though it has two enantiomeric conformations.

Question 45

Draw the R isomer of this compound.

Question 46

d-Sucrose is common table sugar.Its enantiomer, l-sucrose, has been investigated as a
nonnutritive sweetener.Explain why l-sucrose would function as a sweetener, but would not
generate the same number of dietician's calories as the d-enantiomer.

Question 47

Sucrose has a specific rotation of +66.5° at 25° . A solution of an unknown pure substance in ethanol (c=4.62 g/10 mL) shows an observed rotation of +20.4°. Is it possible that the substance is sucrose? Recall that [α]=α/cl , where [α] is the specific rotation, α is the observed rotation, the path length, l , is 1 decimeter; and c is the concentration of the sample.

Question 48

Draw the S enantiomer of 3,3,4-trimethylhexane.

Question 49

Draw the two major products of the addition reaction below, showing stereochemistry. What is the stereochemical relationship between the two products? Are both products optically
active?

Question 50

Define optical activity.

Question 51

Draw all stereoisomers of the molecule shown here.

Question 52

For each pair of molecules, identify whether the pairs are enantiomers, diastereomers, or the same
compound/conformers.

Question 53

Draw a staggered Newman projection of R-2-pentanol looking down the C2-C3 bond.

Question 54

Label each of the following molecules as chiral, achiral, or achiral and meso.

Question 55

Assign the absolute configuration of the stereogenic center in the molecule shown here.

Question 56

Draw all diastereomers of the molecule shown here.

Question 57

Draw the structure of (3R, 4S)-2,3,4 -trimethylheptane.

Question 58

Identify all stereogenic carbon atoms in the molecule shown here and assign the absolute
configuration of each.

Question 59

What are the differences in the physical properties of a pair of enantiomers?

Question 60

Assign the absolute configuration of each stereogenic center in the natural product shown as R
or S.

Question 61

Draw all possible stereoisomers having the skeletal formula shown here.Show stereochemistry
using wedge and dash notation.

Question 62

For the following compounds determine if a) they have one or more stereogenic atoms and b)
they are chiral.

Question 63

Identify each pair of molecules as conformational isomers, diastereomers, enantiomers, identical,
or structural isomers.

Question 64

Dextromethorphan (D-meth) and its enantiomer, levomethorphan (L-meth), have very different
pharmacological effects.D-meth is the active ingredient in many cough suppressants, while
L-meth is an opioid analgesic.Explain how R-mandelic acid could be used to resolve a mixture of
these two drugs if they were produced as a racemic mixture.

Question 65

Explain why compound A is chiral but compound B is not.

Question 66

Draw all stereoisomers of the compound shown and label all stereogenic carbon atoms as R or S.

Question 67

Identify each pair of molecules as conformational isomers, diastereomers, enantiomers, identical,
or structural isomers.

Question 68

Draw all stereoisomers of the molecule shown here.