1. Chapter 3 - Stereoisomerism and Chirality

2. Chapter Outline (3.1) Chirality—the handedness of molecules
(3.2) Stereoisomerism
(3.3) Naming chiral centers—the R,S system
(3.4) Acyclic molecules with two or more stereocenters
(3.5) Cyclic molecules with two or more chiral centers
(3.6) Tying all the terminology together
(3.7) Optical activity—how chirality is detected in the laboratory

3. Chapter Outline (continued)
(3.8) The significance of chirality in the biological world
(3.9) Separation of enantiomers—resolution

4. Chirality
Chiral: Objects that are not superposable on their mirror images
Achiral: Objects that lack chirality and are superposable on their mirror images
Objects have one or more elements of symmetry
Plane of symmetry: Imaginary plane passing through an object dividing it so that one half is the mirror image of the other half
Center of symmetry: A point so situated that identical components of an object are located on opposite sides and equidistant from that point along any axis passing through it
(3‑1) Balancing oxidation–reduction equations

5. Figure 3.1 - Symmetry in Objects
(3‑1) Balancing oxidation–reduction equations

6. Plane of Symmetry - Example
(3‑1) Balancing oxidation–reduction equations

7. Join In (1)
Which of the following molecules possesses a plane of symmetry?
Only A
Only B
Only C
A and C
B and C
(3‑1) Balancing oxidation–reduction equations
Correct answer
A and C

8. Join In (2)
What is the relationship between the two compounds shown below?
They are identical
They are constitutional isomers
They are nonsuperposable mirror images of each other
They are different conformations of the same compound
They have different atom connectivity
(3‑1) Balancing oxidation–reduction equations
Correct Answer
3. They are nonsuperposable mirror images of each other

9. Isomers Different compounds with the same molecular formula
Constitutional isomers - Isomers with a different connectivity of atoms in their molecules
Stereoisomers: Isomers with the same connectivity but different orientations of their atoms in space
Configurational isomers: Isomers that differ by the configuration of substituents on an atom
(3‑2) Stereoisomerism

10. Stereocenter and Chiral Center
Stereocenter: An atom about which exchange of two groups produces a stereoisomer
Chiral center: A tetrahedral atom, most commonly carbon, that is bonded to four different groups
All chiral centers are stereocenters, but not all stereocenters are chiral centers
(3‑2) Stereoisomerism

11. Chiral Centers
Chirality can be present in molecules without chiral centers
Condition occurs via conformational isomerism
Example of a chiral nitrogen center
(3‑2) Stereoisomerism

12. Stereoisomers Are either diastereomers or enantiomers
Enantiomers: Stereoisomers that are nonsuperposable mirror images of each other
Refer to a relationship between pairs of objects
Diastereomers: Stereoisomers that are not mirror images of each other
Refer to the relationship among two or more objects that are either chiral or achiral
Example - Butane is not a chiral molecule
Gauche and anti forms of butane are diastereomers
Two gauche forms are enantiomers
(3‑2) Stereoisomerism

13. Enantiomers - Example 2-Butanol Has one stereocenter
Here are four equivalent representations for one enantiomer
Here are two representations for the enantiomer of (4)
(3‑2) Stereoisomerism

14. Enantiomers - Example (continued 1)
2-Chlorobutane
(3‑2) Stereoisomerism

15. Enantiomers - Example (continued 2)
3-Chlorocyclohexene
(3‑2) Stereoisomerism

16. Atropisomers
Enantiomers that lack a chiral center and differ because of hindered rotation
Example - Substituted biphenyl
(3‑2) Stereoisomerism

17. Example 3.1 - Stereoisomers
Draw stereorepresentations for the enantiomers of each molecule given below
Each molecule has one chiral center
(3‑2) Stereoisomerism

18. Example Solution
It is helpful to view models of enantiomer pairs from different perspectives, as is done in these representations
Notice that each has a tetrahedral carbon atom bonded to four different groups, which makes the molecule chiral
(3‑2) Stereoisomerism

19. Join In (3) Which of the structures below are identical? Only A and C
Only B and D
Only A and D
Only B, C, and D
All are the same
(3‑2) Stereoisomerism
Correct Answer
5. All are the same

20. Join In (4)
Which of the following statements about enantiomers is false?
They have identical melting points
They have identical boiling points
The magnitude of their specific rotations is identical
They have identical densities
They react at the same rate with optically active reagents
(3‑2) Stereoisomerism
Correct Answer
They react at the same rate with optically active reagents

21. R,S System Priority rules
Each atom bonded to the chiral center is assigned a priority based on atomic number
Higher the atomic number, higher the priority
If priority cannot be assigned as per the atoms bonded to the chiral center, look at the next set of atoms
Continue until a priority can be assigned
Priority is assigned at the first point of difference
(3‑3) Naming chiral centers—the R,S system

22. R,S System (continued)
Atoms participating in a double or triple bond are considered to be bonded to an equivalent number of similar atoms by single bonds
Do not assume that larger groups must always have higher priority
(3‑3) Naming chiral centers—the R,S system

23. Example 3.2 - Cahn, Ingold, Prelog Priorities
Assign priorities to the groups in each set
(3‑3) Naming chiral centers—the R,S system

24. Example Solution (a)
The first point of difference is O of the —OH in the carboxyl group compared to —H in the aldehyde group
The carboxyl group has a higher priority
(3‑3) Naming chiral centers—the R,S system

25. Example Solution (b)
Carbon 1 in each group has the same pattern of atoms; namely C(C,C,H) (i.e., carbon bonded to two carbons and a hydrogen)
For the vinyl group, bonding at carbon 2 is C(C,H,H)
For the isopropyl group, at carbon 2, it is C(H,H,H)
The vinyl group is higher in priority than is the isopropyl group
(3‑3) Naming chiral centers—the R,S system

26. Naming Chiral Centers
Locate the chiral center, and identify its four substituents
Assign priority from 1 (highest) to 4 (lowest) to each substituent
Orient the molecule so that the group of lowest priority (4) is directed away from you
Read the three groups projecting toward you in order from highest priority (1) to lowest priority (3)
If the groups are read clockwise, the configuration is R
If they are read counterclockwise, the configuration is S
(3‑3) Naming chiral centers—the R,S system

27. Example 3.3 - R,S Configurations
Assign an R or S configuration to the chiral center in each molecule
(3‑3) Naming chiral centers—the R,S system

28. Example Solution
View each molecule through the chiral center along the bond from the chiral center toward the group of lowest priority
In (a), the order of priority is Cl > CH2CH3 > CH3 > H and the configuration is S
In (b), the order of priority is Cl > CH ═ CH > CH2 > H and the configuration is R
In (c), the order of priority is OH > CH2COOH > CH2CH2OH > CH3 and the configuration is R
(3‑3) Naming chiral centers—the R,S system

29. Join In (5)
What are the absolute configurations of the chiral centers in the molecule shown below?
​1: R; 2: R
1: R; 2: S
1: S; 2: S
1: S; 2: R
Compound does not have chiral centers because of the ring structure
(3‑3) Naming chiral centers—the R,S system
Correct Answer
4. 1: S, 2: R

30. Enantiomers and Diastereomers
For a molecule with n chiral centers, a maximum of 2n stereoisomers are possible
For a molecule with 1 chiral center, 21 = 2 stereoisomers are possible
For a molecule with 2 chiral centers, a maximum of 22 = 4 stereoisomers are possible
Example - 2,3,4-trihydroxybutanal can have a maximum of 22 = 4 stereoisomers (two pairs of enantiomers)
(3‑4) Acyclic molecules with two or more stereocenters

31. Example 3.4 - R and S Assignments
Following are stereorepresentations for the four stereoisomers of 1,2,3-butanetriol
R and S configurations are given for the chiral centers in (1) and (4)
Write the IUPAC names for each compound showing the R or S configuration of each chiral center
Which molecules are enantiomers?
Which molecules are diastereomers?
(3‑4) Acyclic molecules with two or more stereocenters

32. Example 3.4 - Solution (a) and (b)
(2S,3S)-1,2,3-Butanetriol
(2S,3R)-1,2,3-Butanetriol
(2R,3S)-1,2,3-Butanetriol
(2R,3R)-1,2,3-Butanetriol
Solution (b)
Enantiomers are stereoisomers that are nonsuperposable mirror images
From their configurations, it can be seen that compounds (1) and (4) are one pair of enantiomers and compounds (2) and (3) are a second pair of enantiomers
(3‑4) Acyclic molecules with two or more stereocenters

33. Example Solution (c)
Diastereomers are stereoisomers that are not mirror images
Compounds (1) and (2), (1) and (3), (2) and (4), and (3) and (4) are pairs of diastereomers
Diagram that shows the relationships among these isomers
(3‑4) Acyclic molecules with two or more stereocenters

34. Meso Compound
An achiral compound possessing two or more chiral centers that also has chiral isomers
Example - 2,3-dihydroxybutanedioic acid
Has two chiral centers and thus 22 = 4 stereoisomers are possible, but only three stereoisomers exist
(c) and its mirror image are superposable, and thus (c) is achiral
(3‑4) Acyclic molecules with two or more stereocenters

35. Properties of Stereoisomers
Enantiomers have identical physical and chemical properties in achiral environments
Diastereomers have different physical and chemical properties, even in achiral environments
(3‑4) Acyclic molecules with two or more stereocenters

36. Example 3.5 - Stereoisomerism
Following are stereorepresentations for the three stereoisomers of 2,3-butanediol
The carbons are numbered beginning from the left, as shown in (1)
Assign an R or S configuration to each chiral center
Which are enantiomers?
Which are diastereomers?
Which is the meso compound?
(3‑4) Acyclic molecules with two or more stereocenters

37. Example 3.5 - Solution (a), (b), and (c)
(2R,3R)-2,3-Butanediol
(2R,3S)-2,3-Butanediol
(2S,3S)-2,3-Butanediol
Solution (b)
Compounds (1) and (3) are enantiomers
Solution (c)
(1) and (2) are diastereomers
(2) and (3) are also diastereomers
(3‑4) Acyclic molecules with two or more stereocenters

38. Example 3.5 - Solution (d) Compound (2) is a meso compound
Note that compound (2) can be drawn in two symmetric conformations, one of which has a plane of symmetry and the other of which has a center of symmetry
(3‑4) Acyclic molecules with two or more stereocenters

39. Fischer Projections
Two-dimensional representations used to show the configuration of molecules with multiple chiral centers, especially carbohydrates
Imply that the groups to each side are in front and those at top and bottom are behind the plane of the paper
Rotations by 90°are not permissible
(3‑4) Acyclic molecules with two or more stereocenters

40. Writing Fischer Projection
Draw a three-dimensional representation of the molecule oriented so that the vertical bonds from the chiral center are directed away from you and horizontal bonds are directed toward you
Write the molecule as a two-dimensional figure with the chiral center indicated by the point at which the lines cross
The only atom in the plane of the paper is the chiral center
(3‑4) Acyclic molecules with two or more stereocenters

41. Example 3.6 - Fischer Projections
Draw a Fischer projection of (2R,3R)-erythrose
Solution
(3‑4) Acyclic molecules with two or more stereocenters

42. Join In (6) How many meso dibromocyclopentanes, C5H8Br2, are there? 11 2 3 4
(3‑4) Acyclic molecules with two or more stereocenters
Correct Answer
3. 2

43. Join In (7)
How many different meso compounds will be produced by the following reaction (assuming there are no carbocation rearrangements)? 1 2 3 4 5
(3‑4) Acyclic molecules with two or more stereocenters
Correct Answer
1. 1

44. Disubstituted Derivatives of Cyclopentane
2-Methylcyclopentanol
Has 2 chiral centers
Both the cis isomer and the trans isomer are chiral and are diastereomers
Cis isomer exists as one pair of enantiomers
Trans isomer exists as a second pair of enantiomers
(3‑5) Cyclic molecules with two or more chiral centers

45. Disubstituted Derivatives of Cyclopentane (continued)
1,2-Cyclopentanediol
Has 2 chiral centers
22 = 4 stereoisomers are possible, but only three stereoisomers exist
Cis isomer is achiral (meso) because it and its mirror image are superposable
Trans isomer is chiral and exists as a pair of enantiomers
(3‑5) Cyclic molecules with two or more chiral centers

46. Disubstituted Derivatives of Cyclohexane
3-Methylcyclohexanol
Has two chiral centers and exists as 22 = 4 stereoisomers
Cis isomer exists as one pair of enantiomers
Trans isomer exists as a second pair of enantiomers
(3‑5) Cyclic molecules with two or more chiral centers

47. Disubstituted Derivatives of Cyclohexane (continued)
cis-3-Methylcyclohexanol (a pair of enantiomers)
trans-3-Methylcyclohexanol (a pair of enantiomers)
(3‑5) Cyclic molecules with two or more chiral centers

48. Example 3.8 - Stereoisomerism with Rings II
How many stereoisomers exist for 1,3-cyclohexanediol?
(3‑5) Cyclic molecules with two or more chiral centers

49. Example Solution
1,3-Cyclohexanediol has two chiral centers and, according to the 2n rule, has a maximum of 22 = 4 stereoisomers
Trans isomer of this compound exists as a pair of enantiomers
Cis isomer has a plane of symmetry and is a meso compound
Although the 2n rule predicts a maximum of four stereoisomers for 1,3-cyclohexanediol, only three exist: one meso compound and one pair of enantiomers
(3‑5) Cyclic molecules with two or more chiral centers

50. Join In (8)
How many stereogenic centers are present in the following molecule? 1 2 4 7
(3‑5) Cyclic molecules with two or more chiral centers
Correct Answer
5. 7

51. Join In (9)
Despite its name, ascorbic acid (vitamin C) is not a carboxylic acid, but rather has the structure shown below
How many stereoisomers of this compound are possible? 1 2 3 4 8
(3‑5) Cyclic molecules with two or more chiral centers
Correct Answer
4. 4

52. Join In (10)
How many stereoisomers exist for the molecule shown below? 1 2 3 4 8
(3‑5) Cyclic molecules with two or more chiral centers
Correct Answer
4. 4

53. Join In (11) How many stereoisomers exist for 5-methylhepta-2,3-diene?4 8
(3‑5) Cyclic molecules with two or more chiral centers
Correct Answer
4. 4

54. Figure 3.5 - Relationships among Isomers along with Chemical Examples
(3‑6) Tying all the terminology together

55. Detecting Chirality - Plane-Polarized Light
Light oscillating in only a single plane
Ordinary light consists of waves vibrating in all planes perpendicular to its direction of propagation
Optically active: Refers to a compound that rotates the plane of plane-polarized light
Vector sum of left and right circularly polarized light that propagates through space as left- and right-handed helices
Each component interacts in an opposite way with chiral molecules
Results in each member of a pair of enantiomers rotating the plane of polarized light in an opposite direction
(3‑7) Optical activity—how chirality is detected in the laboratory

56. Figure 3.6 - Plane-Polarized Light Is a mixture of Left and Right Circularly Polarized Light
(3‑7) Optical activity—how chirality is detected in the laboratory

57. Detecting Chirality - Polarimeter
Device for measuring the ability of a compound to rotate the plane of polarized light
(3‑7) Optical activity—how chirality is detected in the laboratory

58. Using the Polarimeter
Sample tube filled with solvent is placed in the polarimeter
Analyzing filter is adjusted so that the field is dark
Position of the analyzing filter is taken as 0°
When a solution of an optically active compound is placed in the sample tube, some light passes through the analyzing filter
Optically active compound has rotated the plane of polarized light from the polarizing filter so that it is now no longer at an angle of 90° to the analyzing filter
Analyzing filter is then rotated to restore darkness in the field of view
(3‑7) Optical activity—how chirality is detected in the laboratory

59. Observed Rotation
Number of degrees, , through which a compound rotates the plane of polarized light
Dextrorotatory: Substance that rotates the plane of polarized light to the right and is denoted by (+)
Levorotatory: Substance that rotates the plane of polarized light to the left and is denoted by (−)
Magnitude for a particular compound depends on:
Its concentration
Length of the sample tube
Temperature
Solvent
Wavelength of the light used
(3‑7) Optical activity—how chirality is detected in the laboratory

60. Specific Rotation
Observed rotation of the plane of polarized light when a sample is placed in a tube 1.0 dm in length and at a concentration of 1 g/mL
For a pure liquid, Concentration is expressed in grams per milliliter (g/mL)

61. Example 3.9 - Specific Rotation
A solution is prepared by dissolving 400 mg of testosterone, a male sex hormone, in 10.0 mL of ethanol and placing it in a sample tube 10.0 cm in length
The observed rotation of this sample at 25° C using the D line of sodium is +4.36°
Calculate the specific rotation of testosterone

62. Example Solution
Concentration of testosterone is 400 mg/10.0 mL = g/mL
Length of the sample tube is 1.00 dm
Inserting these values in the equation for calculating specific rotation gives

63. Detecting Chirality - Racemic Mixture and Achiral Molecules
Racemic Mixture: An equimolar mixture of two enantiomers indicated by the prefix (±) or (d, l)
Specific rotation is zero because it contains equal numbers of dextrorotatory and levorotatory molecules
Optically inactive
Achiral molecules
Rotate a plane of polarized light, but light incident from the opposite direction will be rotated by exactly equal and opposite amounts
Light in effect will be incident from all directions on the tumbling molecules because of the random orientation of molecules in a solution
Net optical activity will be zero

64. Ways to Describe the Composition of a Mixture of Enantiomers
Optical purity
Specific rotation of a mixture of enantiomers divided by the specific rotation of the enantiomerically pure substance when they are at the same concentration
Enantiomeric excess: Difference between the percentage of two enantiomers in a mixture
Optical purity is numerically equal to enantiomeric excess, but is experimentally determined
(3‑7) Optical activity—how chirality is detected in the laboratory

65. Example 3.10 - Enantiomeric Excess
Figure 3.9 presents a scheme for separation of the enantiomers of mandelic acid
Specific rotation of optically pure (S)-(−)-mandelic acid is −158
Suppose that instead of isolating pure (S)-(−)-mandelic acid from this scheme, the sample is a mixture of enantiomers with a specific rotation of −134
For this sample, calculate the following:
The enantiomeric excess of this sample of (S)-(2)-mandelic acid
The percentage of (S)-(−)-mandelic acid and of (R)-(+)-mandelic acid in the sample

66. Example Solution
The enantiomeric excess of (S)-(−)-mandelic acid is 84.8%
This sample is 84.8% (S)-(−)-mandelic acid and 15.2% (R,S)-mandelic acid
The (R,S)-mandelic acid is 7.6% S enantiomer and 7.6% R enantiomer
The sample, therefore, contains 92.4% of the S enantiomer and 7.6% of the R enantiomer

67. Example 3.10 - Solution (continued)
We can check these values by calculating the observed rotation of a mixture containing 92.4% (S)-(2)-mandelic acid and 7.6% (R)-(1)-mandelic acid as follows:
This agrees with the experimental specific rotation

68. Problem 3.10
One commercial synthesis of naproxen gives the enantiomer shown in 97% enantiomeric excess
Naproxen is the active ingredient in Aleve and a score of other over-the-counter and prescription nonsteroidal anti-inflammatory drug preparations
Assign an R or S configuration to this enantiomer of naproxen
What are the percentages of R and S enantiomers in the mixture?
(3‑7) Optical activity—how chirality is detected in the laboratory

69. Join In (12)
Which of the following statements about chirality and optical activity is false?
If a solution shows optical activity, it must have a compound present whose mirror image is not superposable on the compound itself
Molecules with a plane of symmetry will show no optical activity
The angle of rotation of plane-polarized light depends on how many chiral molecules the light interacts with while passing through the sample
Enantiomers will always have opposite signs of optical rotation
The R enantiomers are dextrorotatory
(3‑7) Optical activity—how chirality is detected in the laboratory
Correct Answer
5. The R enantiomers are dextrorotatory

70. Join In (13) Which of the molecules given below are achiral? A and C
A and E
B and C
B and D
D and E
(3‑7) Optical activity—how chirality is detected in the laboratory
Correct Answer
2. A and E

71. Join In (14)
An aqueous solution of A (one stereoisomer) and B (one stereoisomer) shows no optical activity
A and B are stereoisomers
Which statement cannot be true?
A and B are diastereomers
A and B are not superposable
A and B are enantiomers
A is meso, and B is chiral
A and B are E and Z isomers
(3‑7) Optical activity—how chirality is detected in the laboratory
Correct Answer
4. A is meso, and B is chiral

72. Join In (15) What is the relation between the following two compounds?
Diastereomers
Enantiomers
Identical
Constitutional isomers
Meso
(3‑7) Optical activity—how chirality is detected in the laboratory
Correct Answer
1. Diastereomers

73. Join In (16)
How many prochirality center(s) do/does 1-butanol (CH3CH2CH2CH2OH) have?
None 1 2 3 4
(3‑7) Optical activity—how chirality is detected in the laboratory
Correct Answer
4. 3

74. Chirality in the Biological World
Except for inorganic salts and a few low-molecular-weight organic substances, the majority of molecules in living systems are chiral
Although these molecules can exist as a number of stereoisomers, generally, only one is found in a given biological system
(3‑8) The significance of chirality in the biological world

75. Chirality in the Biological World (continued)
Enzymes are like hands in a handshake
The substrate fits into a binding site on the enzyme surface
A left-handed molecule, like hands in gloves, will only fit into a left-handed binding site, and a right-handed molecule will only fit into a right-handed binding site
Enantiomers have different physiological properties because of the differences in their interactions with other chiral molecules in living systems
(3‑8) The significance of chirality in the biological world

76. Chirality in Enzymes Chymotrypsin
Enzyme in the intestines of animals, which catalyzes the hydrolysis of proteins during digestion
Human chymotrypsin contains 268 chiral centers
Maximum number of stereoisomers possible is 2268
Only one of the possible stereoisomers of chymotrypsin is produced because each chiral amino acid is only present as a single stereoisomer
Most enzymes either produce or react only with substances that are single stereoisomers (if chiral) because they are chiral substances and are present as single stereoisomers
(3‑8) The significance of chirality in the biological world

77. How an Enzyme Distinguishes between a Molecule and Its Enantiomer
Enzyme with a specific binding site for a molecule with a chiral center can distinguish between a molecule and its enantiomer or one of its diastereomers
Interactions between molecules in living systems take place in a chiral environment
Results in a molecule and its enantiomer or diastereomers having different physiological properties
Interactions between molecules in the biological world are highly enantioselective
(3‑8) The significance of chirality in the biological world

78. Figure 3.8 - Schematic Diagram of an Enzyme Surface with Binding Sites
(3‑8) The significance of chirality in the biological world

79. Join In (17) E-3-Hexene reacts with one equivalent of HBr
If there are no carbocation rearrangements, how many different isomeric products (including stereoisomers) will form? 1 2 3 4 5
(3‑8) The significance of chirality in the biological world
Correct Answer
2. 2

80. Join In (18)
Which is the best accounting for the stereochemistry of the product formed by adding of HCl to (R)-4-chloro-1-pentene?
Two enantiomers in equal amounts
Two enantiomers in different amounts
Two diastereomers in equal amounts
Two diastereomers in different amounts
Three stereoisomers, two of them in equal amounts
(3‑8) The significance of chirality in the biological world
Correct Answer
4. Two diastereomers in different amounts

81. Join In (19)
Which of the following structures represents the lowest energy form of (1S, 3S)-3-chloromethylcyclohexane?
(3‑8) The significance of chirality in the biological world
Correct Answer
5. Option e

82. Join In (20)
Enantiomers have identical chemical and physical properties in achiral environments, while diastereomers have different properties in chiral and achiral surroundings
What can be deduced based on the observation that A smells like citrus fruits, while B has an odor of pine trees?
(3‑8) The significance of chirality in the biological world

83. Join In (20) (continued) A and B are diastereomers
A and B are an exception to the rule and do not have the same properties
The sense of smell cannot be used to deduce anything about the stereochemistry of A and B
The receptors responsible for smell are chiral
As can be observed by looking into a mirror, our noses are chiral
(3‑8) The significance of chirality in the biological world
Correct Answer
4. The receptors responsible for smell are chiral

84. Resolution by Means of Diastereomeric Salts
Resolution: Separation of a racemic mixture into its enantiomers
A pair of enantiomers is converted into two diastereomers with the aid of an enantiomerically pure chiral resolving agent
Diastereomers formed are different compounds, have different physical properties, and can be separated by physical means and purified
Separated diastereomers are converted back to the individual enantiomers chemically, and the chiral resolving agent is recovered
(3‑9) Separation of enantiomers—resolution

85. Resolution by Means of Diastereomeric Salts (continued 1)
Example - Salt formation
Racemic acids can be resolved using commercially available chiral amines such as (R,S)-1-phenylethanamine
(3‑9) Separation of enantiomers—resolution

86. Figure 3.9 - Resolution of Mandelic Acid
(3‑9) Separation of enantiomers—resolution

87. Resolution by Means of Diastereomeric Salts (continued 2)
Racemic bases can be resolved using chiral resolving agents such as (+)-tartaric acid, (−)-malic acid, and (+)-camphoric acid
(3‑9) Separation of enantiomers—resolution

88. Enzymes as Resolving Agents
Enzymes can produce single enantiomer products as they are chiral
Esterases - Class of enzymes that catalyze the hydrolysis of esters to give an alcohol and a carboxylic acid
(3‑9) Separation of enantiomers—resolution

89. Resolution by Means of Chromatography on a Chiral Substrate
Separation method that involves passing a vapor or solution mixture through a column packed with a material with different affinities for different components of the mixture
Common method of resolving enantiomers
Each enantiomer interacts differently with the chiral molecules of the packing material
Elution time will be different for the two enantiomers
(3‑9) Separation of enantiomers—resolution

90. Amino Acid Stereochemistry
The 20 most common amino acids in the biological world have a central carbon, called an α-carbon, bonded to a hydrogen atom, an amine, and a carboxylic acid
At neutral pH, the amines and carboxylic acids exist as ammonium ions and carboxylates, respectively
In 19 of the 20 amino acids, the α-carbon is a chiral center as there is a fourth group on the central carbon other than hydrogen, referred to as a side chain
(3‑9) Separation of enantiomers—resolution

91. Proteins
Long chains of amino acids covalently bonded together by amide bonds (shown in red here) formed between the carboxyl group of one amino acid to the amine group of another amino acid
(3‑9) Separation of enantiomers—resolution

92. Problem 3.31 Which of the following are meso compounds?
(3‑4) Acyclic molecules with two or more stereocenters

93. Problem Solution
A meso compound is an achiral compound possessing two or more chiral centers that also has chiral isomers
A meso compound has either a plane of symmetry or a center of symmetry
(3‑4) Acyclic molecules with two or more stereocenters

94. Problem 3.31 - Solution (continued)
A meso compound is an achiral compound possessing two or more chiral centers that also has chiral isomers
A meso compound has either a plane of symmetry or a center of symmetry
(3‑4) Acyclic molecules with two or more stereocenters