1. Dr. Wolf's CHM 201 & 202 7-1 Chapter 7 Stereochemistry

2. Dr. Wolf's CHM 201 & 202 7-2 Molecular Chirality: Enantiomers

3. Dr. Wolf's CHM 201 & 202 7-3 A molecule is chiral if its two mirror image forms are not superposable upon one another. ASYMMETRIC! A molecule is achiral if its two mirror image forms are superposable. SYMMETRIC! ChiralityChirality

4. Dr. Wolf's CHM 201 & 202 7-4 Br Cl H F Bromochlorofluoromethane is chiral It cannot be superposed point for point on its mirror image.

5. Dr. Wolf's CHM 201 & 202 7-5 Br Cl H F Bromochlorofluoromethane is chiral H Cl Br F To show nonsuperposability, rotate this model 180° around a vertical axis.

6. Dr. Wolf's CHM 201 & 202 7-6 Br Cl H F Bromochlorofluoromethane is chiral H Cl Br F

7. Dr. Wolf's CHM 201 & 202 7-7 Another look

8. Dr. Wolf's CHM 201 & 202 7-8 are enantiomers with respect to each other and nonsuperposable mirror images are called enantiomers EnantiomersEnantiomers

9. Dr. Wolf's CHM 201 & 202 7-9 Isomers stereoisomers constitutionalisomers

10. Dr. Wolf's CHM 201 & 202 7-10 Isomers stereoisomers constitutionalisomers diastereomers enantiomers

11. Dr. Wolf's CHM 201 & 202 7-11 Chlorodifluoromethane is achiral

12. Dr. Wolf's CHM 201 & 202 7-12 Chlorodifluoromethane is achiral The two structures are mirror images, but are not enantiomers, because they can be superposed on each other.

13. Dr. Wolf's CHM 201 & 202 7-13 The Chirality Center

14. Dr. Wolf's CHM 201 & 202 7-14 a carbon atom with four different groups attached to it also called: chiral center asymmetric center stereocenter stereogenic center The Chirality Center wx y z C

15. Dr. Wolf's CHM 201 & 202 7-15 A molecule with a single chirality center is chiral. Bromochlorofluoromethane is an example. Chirality and chirality centers Cl F BrHC

16. Dr. Wolf's CHM 201 & 202 7-16 A molecule with a single chirality center is chiral. 2-Butanol is another example. Chirality and chirality centers CH 3 OHHC CH 2 CH 3

17. Dr. Wolf's CHM 201 & 202 7-17 Examples of molecules with 1 chirality center CH 3 C CH 2 CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 a chiral alkane

18. Dr. Wolf's CHM 201 & 202 7-18 Examples of molecules with 1 chirality center Linalool, a naturally occurring chiral alcohol OH

19. Dr. Wolf's CHM 201 & 202 7-19 Examples of molecules with 1 chirality center 1,2-Epoxypropane: a chirality center can be part of a ring O H2CH2CH2CH2C CHCH 3 attached to the chirality center are: —H —CH 3 —OCH 2 —CH 2 O

20. Dr. Wolf's CHM 201 & 202 7-20 Examples of molecules with 1 chirality center Limonene: a chirality center can be part of a ring CH 3 H C CH 2 attached to the chirality center are: —H —CH 2 CH 2 —CH 2 CH=C —C=C

21. Dr. Wolf's CHM 201 & 202 7-21 Examples of molecules with 1 chirality center Chiral as a result of isotopic substitution CH 3 C D TH

22. Dr. Wolf's CHM 201 & 202 7-22 A molecule with a single chirality center must be chiral. But, a molecule with two or more chirality centers may be chiral or it may not (Sections 7.10-7.13).

23. Dr. Wolf's CHM 201 & 202 7-23 Symmetry in Achiral Structures

24. Dr. Wolf's CHM 201 & 202 7-24 Symmetry tests for achiral structures Any molecule with a plane of symmetry or a center of symmetry must be achiral.

25. Dr. Wolf's CHM 201 & 202 7-25 A plane of symmetry bisects a molecule into two mirror image halves. Chlorodifluoromethane has a plane of symmetry. Plane of symmetry

26. Dr. Wolf's CHM 201 & 202 7-26 A plane of symmetry bisects a molecule into two mirror image halves. 1-Bromo-1-chloro-2-fluoroethene has a plane of symmetry. Plane of symmetry

27. Dr. Wolf's CHM 201 & 202 7-27 A point in the center of the molecule is a center of symmetry if a line drawn from it to any element, when extended an equal distance in the opposite direction, encounters an identical element. Center of symmetry

28. Dr. Wolf's CHM 201 & 202 7-28 Properties of Chiral Molecules: Optical Activity

29. Dr. Wolf's CHM 201 & 202 7-29 A substance is optically active if it rotates the plane of polarized light. In order for a substance to exhibit optical activity, it must be chiral and one enantiomer must be present in excess of the other. Optical Activity

30. Dr. Wolf's CHM 201 & 202 7-30 LightLight has wave properties periodic increase and decrease in amplitude of wave

31. Dr. Wolf's CHM 201 & 202 7-31 LightLight optical activity is usually measured using light having a wavelength of 589 nm this is the wavelength of the yellow light from a sodium lamp and is called the D line of sodium

32. Dr. Wolf's CHM 201 & 202 7-32 Polarized light ordinary (nonpolarized) light consists of many beams vibrating in different planes plane-polarized light consists of only those beams that vibrate in the same plane

33. Dr. Wolf's CHM 201 & 202 7-33 Nicol prism Polarization of light

34. Dr. Wolf's CHM 201 & 202 7-34  Rotation of plane-polarized light

35. Dr. Wolf's CHM 201 & 202 7-35 observed rotation (  ) depends on the number of molecules encountered and is proportional to: path length (l), and concentration (c) therefore, define specific rotation [  ] as: Specific rotation 100  cl concentration = g/100 mL length in decimeters [  ] =

36. Dr. Wolf's CHM 201 & 202 7-36 a mixture containing equal quantities of enantiomers is called a racemic mixture a racemic mixture is optically inactive (  = 0) a sample that is optically inactive can be either an achiral substance or a racemic mixture Racemic mixture

37. Dr. Wolf's CHM 201 & 202 7-37 an optically pure substance consists exclusively of a single enantiomer enantiomeric excess = % one enantiomer – % other enantiomer % optical purity = enantiomeric excess e.g. 75% (-) – 25% (+) = 50% opt. pure (-) Optical purity

38. Dr. Wolf's CHM 201 & 202 7-38 Absolute and Relative Configuration

39. Dr. Wolf's CHM 201 & 202 7-39 Relative configuration compares the arrangement of atoms in space of one compound with those of another. until the 1950s, all configurations were relative Absolute configuration is the precise arrangement of atoms in space. we can now determine the absolute configuration of almost any compound ConfigurationConfiguration

40. Dr. Wolf's CHM 201 & 202 7-40 No bonds are made or broken at the stereogenic center in this experiment. Therefore, when (+)-3-buten-2-ol and (+)-2-butanol have the same sign of rotation, the arrangement of atoms in space is analogous. The two have the same relative configuration. CH 3 CHCH 2 CH 3 OH H 2, Pd [  ] + 33.2° [  ] + 13.5° Relative configuration CH 3 CHCH OH CH 2

41. Dr. Wolf's CHM 201 & 202 7-41 HHO HOH H 2, Pd HHO HOH Two possibilities But in the absence of additional information, we can't tell which structure corresponds to (+)-3-buten-2-ol, and which one to (–)-3-buten-2-ol.

42. Dr. Wolf's CHM 201 & 202 7-42 HHO HOH H 2, Pd HHO HOH Two possibilities Nor can we tell which structure corresponds to (+)-2-butanol, and which one to (–)-2-butanol.

43. Dr. Wolf's CHM 201 & 202 7-43 HHO HOH H 2, Pd HHO HOH Absolute configurations [  ] +13.5° [  ] +33.2° [  ] –33.2° [  ] –13.5°

44. Dr. Wolf's CHM 201 & 202 7-44 Not all compounds that have the same relative configuration have the same sign of rotation. No bonds are made or broken at the stereogenic center in the reaction shown, so the relative positions of the atoms are the same. Yet the sign of rotation changes. CH 3 CH 2 CHCH 2 Br CH 3 HBr [  ] -5.8° [  ] + 4.0° Relative configuration CH 3 CH 2 CHCH 2 OH CH 3

45. Dr. Wolf's CHM 201 & 202 7-45 The Cahn-Ingold-Prelog R-S Notational System

46. Dr. Wolf's CHM 201 & 202 7-46 1. need rules for ranking substituents at stereogenic center in order of decreasing precedence 2. need convention for orienting molecule so that order of appearance of substituents can be compared with rank The system that is used was devised by R. S. Cahn, Sir Christopher Ingold, and V. Prelog. Two requirements for a system for specifying absolute configuration

47. Dr. Wolf's CHM 201 & 202 7-47 1. Rank the substituents at the stereogenic center according to same rules used in E-Z notation. 2. Orient the molecule so that lowest-ranked substituent points away from you. The Cahn-Ingold-Prelog Rules (Table 7.1)

48. Dr. Wolf's CHM 201 & 202 7-48 4 3 2 1ExampleExample 4 3 2 1 Order of decreasing rank: 4 > 3 > 2 > 1

49. Dr. Wolf's CHM 201 & 202 7-49 1. Rank the substituents at the stereogenic center according to same rules used in E-Z notation.1. Rank the substituents at the stereogenic center according to same rules used in E-Z notation. 2. Orient the molecule so that lowest-ranked substituent points away from you.2. Orient the molecule so that lowest-ranked substituent points away from you. 3. If the order of decreasing precedence traces a clockwise path, the absolute configuration is R. If the path is anticlockwise, the configuration is S.3. If the order of decreasing precedence traces a clockwise path, the absolute configuration is R. If the path is anticlockwise, the configuration is S. The Cahn-Ingold-Prelog Rules (Table 7.1)

50. Dr. Wolf's CHM 201 & 202 7-50 4 3 2 1ExampleExample 4 3 2 1 Order of decreasing rank: 4  3  2 clockwise R anticlockwise S

51. Dr. Wolf's CHM 201 & 202 7-51 (S)-2-Butanol C OH H3CH3CH3CH3CH CH 3 CH 2 Enantiomers of 2-butanol C HO CH 3 H CH 2 CH 3 (R)-2-Butanol

52. Dr. Wolf's CHM 201 & 202 7-52 Very important! Two different compounds with the same sign of rotation need not have the same configuration.

53. Dr. Wolf's CHM 201 & 202 7-53H H3CH3CH3CH3CH H Chirality center in a ring R —CH 2 C=C > —CH 2 CH 2 > —CH 3 > —H

54. Dr. Wolf's CHM 201 & 202 7-54 Fischer Projections Purpose of Fischer projections is to show configuration at chirality center without necessity of drawing wedges and dashes or using models.Purpose of Fischer projections is to show configuration at chirality center without necessity of drawing wedges and dashes or using models.

55. Dr. Wolf's CHM 201 & 202 7-55 Rules for Fischer projections Arrange the molecule so that horizontal bonds at chirality center point toward you and vertical bonds point away from you. Br Cl F H

56. Dr. Wolf's CHM 201 & 202 7-56 Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H

57. Dr. Wolf's CHM 201 & 202 7-57 Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H

58. Dr. Wolf's CHM 201 & 202 7-58 Physical Properties of Enantiomers

59. Dr. Wolf's CHM 201 & 202 7-59 Same: melting point, boiling point, density, etc Different: properties that depend on shape of molecule (biological-physiological properties) can be different Physical properties of enantiomers

60. Dr. Wolf's CHM 201 & 202 7-60 O O CH 3 H3CH3CH3CH3C H3CH3CH3CH3C CH 2 OdorOdor (–)-Carvone spearmint oil (+)-Carvone caraway seed oil

61. Dr. Wolf's CHM 201 & 202 7-61 Ibuprofen is chiral, but normally sold as a racemic mixture. The S enantiomer is the one responsible for its analgesic and antiinflammatory properties. Chiral drugs CH 2 CH(CH 3 ) 2 H H3CH3CH3CH3C C O C HO

62. Dr. Wolf's CHM 201 & 202 7-62 Reactions That Create A Chiral Center

63. Dr. Wolf's CHM 201 & 202 7-63 Many reactions convert achiral reactants to chiral products. It is important to recognize, however, that if all of the components of the starting state (reactants, catalysts, solvents, etc.) are achiral, any chiral product will be formed as a racemic mixture. This generalization can be more simply stated as "Optically inactive starting materials can't give optically active products." (Remember: In order for a substance to be optically active, it must be chiral and one enantiomer must be present in greater amounts than the other.

64. Dr. Wolf's CHM 201 & 202 7-64 ExampleExample CH 3 CH CH 2 CH 3 COOH O H3CH3CH3CH3C O CH 2 CH Chiral, but racemic Achiral

65. Dr. Wolf's CHM 201 & 202 7-65 epoxidation from this direction gives R epoxide R

66. Dr. Wolf's CHM 201 & 202 7-66 epoxidation from this direction gives R epoxide epoxidation from this direction gives S epoxide R S

67. Dr. Wolf's CHM 201 & 202 7-67 50% 50% epoxidation from this direction gives R epoxide epoxidation from this direction gives S epoxide R S

68. Dr. Wolf's CHM 201 & 202 7-68 ExampleExample CH 3 CH CH 2 Chiral, but racemic Br 2, H 2 O CH 3 CHCH 2 Br OH Achiral

69. Dr. Wolf's CHM 201 & 202 7-69 ExampleExample CH 3 CH CHCH 3 Chiral, but racemic HBr CH 3 CHCH 2 CH 3 Br Achiral

70. Dr. Wolf's CHM 201 & 202 7-70 Many reactions convert chiral reactants to chiral products. However, if the reactant is racemic, the product will be racemic also. Remember: "Optically inactive starting materials can't give optically active products."

71. Dr. Wolf's CHM 201 & 202 7-71 ExampleExample Chiral, but racemic HBr CH 3 CHCH 2 CH 3 OH Br Chiral, but racemic

72. Dr. Wolf's CHM 201 & 202 7-72 Many biochemical reactions convert an achiral reactant to a single enantiomer of a chiral product Reactions in living systems are catalyzed by enzymes, which are enantiomerically homogeneous. The enzyme (catalyst) is part of the reacting system, so such reactions don't violate the generalization that "Optically inactive starting materials can't give optically active products."

73. Dr. Wolf's CHM 201 & 202 7-73 ExampleExample fumarase H2OH2OH2OH2O C C HO 2 C H CO 2 H H C OHH HO 2 C HO 2 CCH 2 Fumaric acid (S)-(–)-Malic acid Achiral Single enantiomer

74. Dr. Wolf's CHM 201 & 202 7-74 Chiral Molecules with Two Chirality Centers How many stereoisomers when a particular molecule contains two chiral centers?

75. Dr. Wolf's CHM 201 & 202 7-75 2,3-Dihydroxybutanoic acid What are all the possible R and S combinations of the two chirality centers in this molecule? O CH 3 CHCHCOH HOOH 2 3

76. Dr. Wolf's CHM 201 & 202 7-76 2,3-Dihydroxybutanoic acid What are all the possible R and S combinations of the two chirality centers in this molecule? O CH 3 CHCHCOH HOOH 2 3 Carbon-2RRSS Carbon-3RSRS

77. Dr. Wolf's CHM 201 & 202 7-77 2,3-Dihydroxybutanoic acid 4 Combinations = 4 Stereoisomers O CH 3 CHCHCOH HOOH 2 3 Carbon-2RRSS Carbon-3RSRS

78. Dr. Wolf's CHM 201 & 202 7-78 2,3-Dihydroxybutanoic acid 4 Combinations = 4 Stereoisomers What is the relationship between these stereoisomers? O CH 3 CHCHCOH HOOH 2 3 Carbon-2RRSS Carbon-3RSRS

79. Dr. Wolf's CHM 201 & 202 7-79 2,3-Dihydroxybutanoic acid O CH 3 CHCHCOH HOOH 2 3 Carbon-2RRSS Carbon-3RSRS enantiomers:2R,3R and 2S,3S 2R,3S and 2S,3R

80. Dr. Wolf's CHM 201 & 202 7-80 HO CO 2 H CH 3 H OH H R R CO 2 H CH 3 H H HO OH S S enantiomersenantiomers CO 2 H H CH 3 HO H HO R S CO 2 H CH 3 H OH OH H R S enantiomersenantiomers [  ] = -9.5° [  ] = +9.5° [  ] = -17.8° [  ] = +17.8°

81. Dr. Wolf's CHM 201 & 202 7-81 2,3-Dihydroxybutanoic acid O CH 3 CHCHCOH HOOH 23 Carbon-2RRSS Carbon-3RSRS but not all relationships are enantiomeric stereoisomers that are not enantiomers are: diastereomers……. similar but not identical chemical and physical properties

82. Dr. Wolf's CHM 201 & 202 7-82 Isomers stereoisomers constitutionalisomers diastereomers enantiomers

83. Dr. Wolf's CHM 201 & 202 7-83 HO CO 2 H CH 3 H OH H R R CO 2 H CH 3 H H HO OH S S enantiomersenantiomers CO 2 H H CH 3 HO H HO R S diastereomersdiastereomers CO 2 H CH 3 H OH OH H R S enantiomersenantiomers [  ] = -9.5° [  ] = +9.5° [  ] = -17.8° [  ] = +17.8°

84. Dr. Wolf's CHM 201 & 202 7-84 CO 2 H CH 3 Fischer Projections recall for Fischer projection: horizontal bonds point toward you; vertical bonds point away staggered conformation does not have correct orientation of bonds for Fischer projection

85. Dr. Wolf's CHM 201 & 202 7-85 Fischer projections transform molecule to eclipsed conformation in order to construct Fischer projection

86. Dr. Wolf's CHM 201 & 202 7-86 Fischer projections CO 2 H CH 3 OH OH H H

87. Dr. Wolf's CHM 201 & 202 7-87 Erythro and Threo stereochemical prefixes used to specify relative configuration in molecules with two chirality centers easiest to apply using Fischer projections orientation: vertical carbon chain

88. Dr. Wolf's CHM 201 & 202 7-88 when carbon chain is vertical, same (or analogous) substituents on same side of Fischer projection CO 2 H CH 3 OH OH H H –9.5° +9.5° CO 2 H CH 3 H H HO HO ErythroErythro

89. Dr. Wolf's CHM 201 & 202 7-89 when carbon chain is vertical, same (or analogous) substituents on opposite sides of Fischer projection +17.8° –17.8° OH CO 2 H CH 3 H H HO CO 2 H CH 3 OH H H HO ThreoThreo

90. Dr. Wolf's CHM 201 & 202 7-90 S S R R Two chirality centers in a ring nonsuperposable mirror images; enantiomers trans-1-Bromo-2-chlorocyclopropane

91. Dr. Wolf's CHM 201 & 202 7-91 S R S R Two chirality centers in a ring nonsuperposable mirror images; enantiomers cis-1-Bromo-2-chlorocyclopropane

92. Dr. Wolf's CHM 201 & 202 7-92 S R S R Two chirality centers in a ring stereoisomers that are not enantiomers; diastereomers cis-1-Bromo-2-chloro- cyclopropane trans-1-Bromo-2-chloro- cyclopropane

93. Dr. Wolf's CHM 201 & 202 7-93 Achiral Molecules with Two Chirality Centers It is possible for a molecule to have chirality centers yet be achiral.

94. Dr. Wolf's CHM 201 & 202 7-94 2,3-Butanediol2,3-Butanediol Consider a molecule with two equivalently substituted chirality centers such as 2,3 butanediol. CH 3 CHCHCH 3 HOOH 3 2

95. Dr. Wolf's CHM 201 & 202 7-95 Three stereoisomers of 2,3-butanediol 2R,3R 2S,3S 2R,3S chiralchiralachiral

96. Dr. Wolf's CHM 201 & 202 7-96 Three stereoisomers of 2,3-butanediol 2R,3R 2S,3S 2R,3S chiralchiralachiral CH 3 OH H H HO H OH H HO H OH OH H

97. Dr. Wolf's CHM 201 & 202 7-97 Three stereoisomers of 2,3-butanediol 2R,3R 2S,3S chiralchiral these two are enantiomers

98. Dr. Wolf's CHM 201 & 202 7-98 Three stereoisomers of 2,3-butanediol 2R,3R 2S,3S chiralchiral CH 3 OH H H HO H OH H HO these two are enantiomers

99. Dr. Wolf's CHM 201 & 202 7-99 Three stereoisomers of 2,3-butanediol 2R,3S achiral the third structure is superposable on its mirror image

100. Dr. Wolf's CHM 201 & 202 7-100 Three stereoisomers of 2,3-butanediol 2R,3S achiral therefore, this structure and its mirror image are the same it is called a meso form a meso form is an achiral molecule that has chirality centers

101. Dr. Wolf's CHM 201 & 202 7-101 Three stereoisomers of 2,3-butanediol 2R,3S achiral H CH 3 OH OH H H HO H HO therefore, this structure and its mirror image are the same it is called a meso form a meso form is an achiral molecule that has chirality centers

102. Dr. Wolf's CHM 201 & 202 7-102 Three stereoisomers of 2,3-butanediol 2R,3S achiral meso forms have a plane of symmetry and/or a center of symmetry plane of symmetry is most common case top half of molecule is mirror image of bottom half

103. Dr. Wolf's CHM 201 & 202 7-103 Three stereoisomers of 2,3-butanediol 2R,3S achiral H CH 3 OH OH H H HO H HO A line drawn the center of the Fischer projection of a meso form bisects it into two mirror- image halves.

104. Dr. Wolf's CHM 201 & 202 7-104 S R R Rchiralmeso There are three stereoisomers of 1,2-dichloro- cyclopropane; the achiral (meso) cis isomer and two enantiomers of the trans isomer. Cyclic compounds

105. Dr. Wolf's CHM 201 & 202 7-105 Molecules with Multiple Chirality Centers

106. Dr. Wolf's CHM 201 & 202 7-106 maximum number of stereoisomers = 2 n where n = number of structural units capable of stereochemical variation structural units include chirality centers and cis and/or trans double bonds number is reduced to less than 2 n if meso forms are possible How many stereoisomers?

107. Dr. Wolf's CHM 201 & 202 7-107 ExampleExample 4 chirality centers 16 stereoisomers O HOCH 2 CH—CH—CH—CHCH OHOHOHOH

108. Dr. Wolf's CHM 201 & 202 7-108 HO OH H H HO H3CH3CH3CH3C H H CH 2 CH 2 CO 2 H CH 3 H 11 chirality centers 2 11 = 2048 stereoisomers one is "natural" cholic acid a second is the enantiomer of natural cholic acid 2046 are diastereomers of cholic acid Cholic acid

109. Dr. Wolf's CHM 201 & 202 7-109 maximum number of stereoisomers = 2 n where n = number of structural units capable of stereochemical variation structural units include chirality centers and cis and/or trans double bonds number is reduced to less than 2 n if meso forms are possible How many stereoisomers?

110. Dr. Wolf's CHM 201 & 202 7-110 3-Penten-2-ol HO H E R H OH E S H HO Z R H OH S How many stereoisomers? Z

111. Dr. Wolf's CHM 201 & 202 7-111 Chemical Reactions That Produce Diastereomers

112. Dr. Wolf's CHM 201 & 202 7-112 In order to know understand stereochemistry of product, you need to know two things: (1) stereochemistry of alkene (cis or trans; Z or E) (1) stereochemistry of alkene (cis or trans; Z or E) (2) stereochemistry of mechanism (syn or anti) (2) stereochemistry of mechanism (syn or anti) Stereochemistry of Addition to Alkenes C C + E—Y C C E Y

113. Dr. Wolf's CHM 201 & 202 7-113 Br 2 R S R S meso anti addition to trans-2-butene gives meso diastereomer Bromine Addition to trans-2-Butene

114. Dr. Wolf's CHM 201 & 202 7-114 Br 2 R R S S 50%50% Bromine Addition to cis-2-Butene anti addition to cis-2-butene gives racemic mixture of chiral diastereomer +

115. Dr. Wolf's CHM 201 & 202 7-115 RCO 3 H R R S S syn addition to trans-2-butene gives racemic mixture of chiral diastereomer Epoxidation of trans-2-Butene 50%50% +

116. Dr. Wolf's CHM 201 & 202 7-116 R S R S Epoxidation of cis-2-Butene syn addition to cis-2-butene gives meso diastereomer RCO 3 H meso

117. Dr. Wolf's CHM 201 & 202 7-117 Of two stereoisomers of a particular starting material, each one gives different stereoisomeric forms of the product Related to mechanism: terms such as syn addition and anti addition refer to stereospecificity Stereospecific reaction

118. Dr. Wolf's CHM 201 & 202 7-118. trans-2-butene cis-2-butene trans-2-butene cis-2-butene brominationanti 2R,3R + 2S,3S bromination epoxidation epoxidation anti syn syn meso meso Stereospecific reactions

119. Dr. Wolf's CHM 201 & 202 7-119 A single starting material can give two or more stereoisomeric products, but gives one of them in greater amounts than any other + CH 3 H H 68% 32% Stereoselective reaction CH 3 CH 2 H CH 3 H H H2H2H2H2Pt

120. Dr. Wolf's CHM 201 & 202 7-120 Resolution of Enantiomers Separation of a racemic mixture into its two enantiomeric forms

121. Dr. Wolf's CHM 201 & 202 7-121 enantiomersC(+)C(+)C(-)C(-)StrategyStrategy

122. Dr. Wolf's CHM 201 & 202 7-122 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers StrategyStrategy

123. Dr. Wolf's CHM 201 & 202 7-123 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers C(+) C(+)P(+) C(-) C(-)P(+) StrategyStrategy

124. Dr. Wolf's CHM 201 & 202 7-124 enantiomersC(+)C(+)C(-)C(-) 2P(+) C(+) C(+)P(+) C(-) C(-)P(+) diastereomers C(+) C(+)P(+) C(-) C(-)P(+) P(+) C(+)C(+) C(-)C(-) StrategyStrategy

125. Dr. Wolf's CHM 201 & 202 7-125 Stereoregular Polymers atacticisotacticsyndiotactic

126. Dr. Wolf's CHM 201 & 202 7-126 Atactic Polypropylene random stereochemistry of methyl groups attached to main chain (stereorandom) properties not very useful for fibers etc. formed by free-radical polymerization

127. Dr. Wolf's CHM 201 & 202 7-127 Isotactic Polypropylene stereoregular polymer; all methyl groups on same side of main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

128. Dr. Wolf's CHM 201 & 202 7-128 Syndiotactic Polypropylene stereoregular polymer; methyl groups alternate side-to-side on main chain useful properties prepared by coordination polymerization under Ziegler-Natta conditions

129. Dr. Wolf's CHM 201 & 202 7-129 Chirality Centers Other Than Carbon

130. Dr. Wolf's CHM 201 & 202 7-130 SiliconSilicon Silicon, like carbon, forms four bonds in its stable compounds and many chiral silicon compounds have been resolved SiSi dd a b c a b c

131. Dr. Wolf's CHM 201 & 202 7-131 Nitrogen in amines Pyramidal geometry at nitrogen can produce a chiral structure, but enantiomers equilibrate too rapidly to be resolved NN :: a b c a b c very fast

132. Dr. Wolf's CHM 201 & 202 7-132 Phosphorus in phosphines Pyramidal geometry at phosphorus can produce a chiral structure; pyramidal inversion slower than for amines and compounds of the type shown have been resolved PP :: a b c a b c slow

133. Dr. Wolf's CHM 201 & 202 7-133 Sulfur in sulfoxides Pyramidal geometry at sulfur can produce a chiral structure; pyramidal inversion is slow and compounds of the type shown have been resolved SS :: a b O_ a b O_ slow ++

134. Dr. Wolf's CHM 201 & 202 7-134 End of Chapter 7