1. Chapter 5 Stereochemistry（立体化学）: Chiral Molecules（手性分子）
5.1 Isomerism: Constitutional isomers and Stereoisomers (构形异构与立体异构）

4. 5.2 Enantiomers and chiral molecules
A Chiral molecule is defined as one that is not superposable on its mirror image.
The chiral molecule and its mirror image are enantiomers, and the relationship between the chiral molecule and its mirror image is defined as enantiomeric (对映异构）.
The word chiral comes from the Greek word Cheir, meaning ‘hand’. That means, relationship between left hand and right hand.

5. 5.2 Chiral molecules (手性分子)
Left hand (左手)和right hand(右手)
相似而不重合

6. Because models I and II are nonsuperposable mirror images of each other, the molecules that they represent are enantiomers.

7. Problem 5.1 Classify the following objects as to whether they are chiral (手性） or achiral（非手性）
(a) Screw ( b) plain spoon (c ) Fork
(d) Cup (e) Foot (f) Ear
(g) Shoe (h) Spiral staircase（螺旋梯）

8. Problem 5.2
(a) If models are available, construct the 2-butanols represented in Fig. 5.3 and demonstrate for yourself that they are not mutually superposable.
(b) Make similar models of 2-propanol (CH3CHOHCH3). Are they superposable?
(c ) Is 2-propanol chiral?
(d) Would you expect to find enantiomeric forms of 2-propanol?

10. one tetrahedral atom with four different groups attached to carbon, it is called chiral carbon（手性碳）
(a) CH3CHClCH3 (b) CH3CHBrCH2CH3
(c ) CH3CHOHCHOHCH3 (d) (CH3)2CHOH
(e) BrCHClI
(f) CH3CH2CHClCH2CH3

11. 5.3 Historical origin of stereochemistry
The following information was available to van’t Hoff and le Bel.
1. Only one compound for CH3X is ever found
2. Only one compound for CH2X2 or CH3XY is ever found.
3. Two enantiomeric compounds for CHXYZ are found.

12. 5.4 Tests for Chirality: Planes of Symmetry( 对称面）
All molecules with a plane of symmetry are achiral
All molecules with no plane of symmetry are chiral

13. 三、对称因素和手性分子判据 1.对称因素 ◎ 对称面σ：可把分子分割成两部分的平面，一部分正好是另一部分的镜象，这个平面称为对称面。 （图）
   ◎ 对称面σ：可把分子分割成两部分的平面，一部分正好是另一部分的镜象，这个平面称为对称面。 （图）
例1：1，1-二氯乙烷
例2：（E）-1，2-二氯乙烯

14. Problem 5.7 Write three-dimensional formulas and designate a plane of symmetry for all of the achiral molecules in Problem 5.4.

16. 5.5 Nomenclature of enantiomers: The (R-S) system

17. Groups containing double or triple bonds

18. Problem 5.11 Assign ( R) or (S) designations to each of the following compounds
(3R) (3R) (3R)

19. Sample problem; Consider the following pair of structures and tell whether they represent enantiomers or two molecules of the same compound in different orientations.

22. Problem Tell whether the two structures in each pair represent enantiomers or two molecules of the same compound in different orientations.
(s) Enantiomers (R)

23. ( R ) Same (R)
(2S)-Butanol Enantiomers (2R)-Butanol

24. ‘十字式’的 R/S 的命名

27. Problem; Assign （ R) or (S) designations to each of the following compounds;

28. 5.6 Properties of enantiomers; Optical Activity (光学活性）
The molecules of enantiomers are not superposable one on the other, and on this basis alone, we have concluded that enantiomers are different compounds. Do enantiomers resemble constitutional isomers and diastereomers in having different melting and boing points? The answer is no. Enantiomers have identical melting and boiling points. Enantiomers have identical (refraction(折射率）, solubilities（溶解度）, infrared spectra（红外光谱） and rates of reaction（反应速率)

29. Table 5.1 Physical properties of ( R )- and ( S )-2-butanol

30. 5.6 A . Plane-polarized light (偏振光）
One easily observable way in which enantiomers differ is in their behavior toward plan-polarized light. When a beam of plane-polarized light passes throught an enantiomer, the plane of polarization rotates. Because of their effect on plane-polarized light, separate enantiomers are said to be optically active compounds.

31. 物质的旋光性(The matter rotation for plane-polarized light)
一、平面偏振光(plane-polarized light)和旋光性(rotation)
The Characteristic of electric wave of light (光波的特点)：
① 振动方向与前进方向垂直(vertical)；
② 在垂直于前进方向的任何可能的平面上振动。
Nicol棱晶(Nicol polarizer)：只允许与晶轴平行的平面上振动的光线透过。
这种只在一个平面上振动的光称为平面偏振光或简称偏振光(plane-polarized light)。

32. 使偏光使振动平面旋转的物质——旋光性物质（光学活性物质(optically active compounds）
使偏光向右旋——右旋体“+”(Levorotatory)
使偏光向左旋——左旋体“-” (Dextrorotatory)
例：肌肉乳酸 (CH3CHOHCOOH) +3.8°
发酵乳酸 (CH3CHOHCOOH) -3.8°

33. Fig. 5.8 The oscillating (振荡） electric and
magnetic fields of a beam of ordinary light in one plane

34. Fig. 5.9 Oscillation of the electrical field of
ordinary light occurs in all possible planes
Perpendicular (垂直）to the direction of propagation （传播）.

36. 5.6B The polarimeter （旋光仪 或偏振仪）
The device that is used for measuring the effect of
plane-polarized light on optically active compounds is a polarimeter

37. Fig 5.11 The principal working parts of a polarimeter and the measurement of optical rotation

38. Fig a polarimeter

40. 5.6 C Specific Rotation (比旋光度）[α]
The number of degrees that the plane of polarization is rotated as the light passes through a solution of an enantiomer depends on the number of chiral molecules that it encounters. This, of course, depends on the length of the tube and the concentration of the enantiomer. In order to place measured rotations on a standard basis, chemists calculate a quantity called the specific rotation [α]

41. Specific Rotation (比旋光度[α])

42. The specific rotations of ( R )-2-butanol and ( S )-2-butanol

43. No necessary correlation exits between the ( R ) and ( S ) designation and the direction of rotation of plane-polarized light

44. 5.7 the origin of optical activity

45. 5.7A Racemic forms (外消旋体)
An equimolar mixture of two enantiomers is called a racemic form (左旋体和右旋体的等量混合物称为外消旋体)

46. Racemic forms (（±）外消旋体)
An equimolar mixture of two enantiomers
(左旋体(levorotatory (-) )和右旋体（dextrorotatory (+) )的等量混合物。（±）)
  The characteristic of racemic forms; (外消旋体的特点)：
1）Chemical property is at same (化性基本相同)；
  2）(No rotation )没有旋光性；
  3）(Biological activity is different for enantiomers)左旋体和右旋体的相应生理作用不同。
（氯霉素的左旋体有杀菌作用，它的右旋体无作用）

47. Meso-Compounds (内消旋体)
The characteristic of meso-Compounds;
1) 旋光在分子的内部抵消（Achiral molecule)；
2）(there is a plane of symmetry) 分子有对称面，没有旋光活性(no rotation)；
3）(No enantiomers) 无对映异构体；

48. 5.7B Enantiomeric purity, optical purity, and enantiomeric excess

49. Enantiomeric excess (对映体过量百分率)（%e.e）：
[R]-[S]
%e.e = ×100% = %R-%S
[R]+[S]
[R]：过量对映体的量
[S]：为其对映体的量

50. Problem What relative molar proportions of ( S )- (+)-2-butanol and ( R)- (-)-2-butanol would give a specific rotation, [α], equal to +6.76o ? (S)-(+)-2-butanol%? And ( R )%?

51. Answer

52. 5.8 The synthesis of enantiomers
The hydrogenation of ketone

53. Fig 5.14. Shows why a racemic form of 2-butanol is obtaned

54. 5.9 Molecules with more than one stereocenter
1) Compounds contain two different chiral carbon (含两个不相同手性碳原子的化合物) 2n

55. ⅠandⅡor III and IV are enantiomers (对映体)；ⅠandⅢ or Ⅳ are diasteromers(为非对映体)；(Ⅱ与Ⅲ或Ⅳ为非对映体)；
2.The charecteristic of diasteromers (非对映异构体的特点)：
1）Physical property , specific rotation is different (物性不同、比旋光度不同)；
2）Chemical property is similar(化性相似，但速度有差异)

56. 二、At the same two chiral carbon (含两个相同手性碳原子的化合物)
1.光学异构体数目
(2n-1);
ⅠandⅡ are enantiomers (对映异构体）；Ⅲ and Ⅳ are at the same compounds)；Ⅰand Ⅲ are diastereomers；ⅡandⅢ are distereomers (非对映体)；Ⅲ is a meso compound (内消旋体)

57. 5.9A Meso Compounds (内消旋化合物）
A structures with two stereocenters will not always have four possible steroisomers. Sometimes there are only three (2n-1). This happens because some molecules with stereocenters are, overall, achiral

58. 2,3-Dibromobutane

59. Problem Write three-dimensional formulas for all of the steroisomers of each of the following compounds. In answer to parts (a)-(e) label pairs of each enantiomers and meso compounds.
( a) CH3CHClCHClCH3
( b) CH3CHBrCHClCH3
( c) CH3CHBrCHBrCH2Br
( d) CH3BrCHBrCHBrCH2Br
( e) CH3CHClCHClCHClCH3

60. 5.10 Naming compounds with more than one stereocenter

61. 5.11 Fischer projection formulas （费歇尔投影式 ）

62. The rotation 180o in plane forms at the same structure

63. 5.12 Stereoisomerism of cyclic compounds

64. Problem Write structural formulas for all of the stereoisomers of 1,3-dimethylcyclopentane. Label pairs of enantiomers and meso commpounds if they exist.

65. 5.12A Cyclohexane derivatives
1) 1,4-Dimethylcyclohexanes

66. Fig 5.17 cis-1,3-Dimethylcyclohexane

67. Fig 5.18 trans-1,3-Dimethylcyclohexane

68. Fig 5.19 trans-1,2-Dimethylcyclohexane

69. Fig 5.20 cis-1,2-Dimethylcyclohexane

70. Problem Write formulas for all of the isomers of each of the following. Designate pairs of enantiomers and achiral compounds where they exist.
( a) 1-Bromo-2-chlorocyclohexane
( b) 1-Bromo-3-chlorocyclohexane
( c) 1-Bromo-4-chlorocyclohexane

71. ( a) 1-Bromo-2-chlorocyclohexane

72. trans-1-Bromo-2-chlorocyclohexane

73. ( c) 1-Bromo-4-chlorocyclohexane

74. 5.13 Relating configurations through reactions in which no bonds to the stereocenter are broken
If a reaction takes places in a way so that no bonds to the stereocenter are broken, the product will of necessity have the same general configuration of groups around the stereocenter as the reactant. Such a reaction is said to proceed with retention of configuration(构形保持）.

75. Consider as an example the reaction that takes place when (S)-(-)-2-methyl-1-butanol is heated with concentrated hydrochloric acid

76. Example---retention of configuration

77. 5.13A Relative and absolute configurations (相对构形和绝对构形）

78. Tartaric acid (酒石酸）

79. 5.14 Separation of enantiomers (对映体的分离）; Resolution (拆分）
How are enantiomers separated?
Enantimores have identical solubilities in ordinary solvents. You couldn’t do crystallzation for separations of racemic form.
You have made diastereomers for each (because they have different melting points, different boing points, and different solubilities) and then resolution for each one

80. 将外消旋体的两个对映体分开使之成为纯净的左旋体或右消旋体-----称为拆分(resolution)。
1.化学法（拆分外消旋（±）Tartaric acid 酒石酸）
2. Biological 生化法

81. 5.15 Compounds with stereocenters other than carbon
Any tetrahedral atom with four different groups attached to it is a stereocenter.
Listed here are general formulas of compounds whose molecules contain stereocenters other than carbon. Silicon and germanium are in the same group of the periodic table as carbon. They form tetrahedral compounds as carbon does.

82. The molecules are chiral and the enantiomers can be separated

83. 5.16 Chiral molecules that do not posses a tetrahedral atom with four different groups(丙二烯型的手性分子）

84. Fig 5.21 Enantiomeric forms of 1,3-dichloroallene

85. Diphenyl compounds(联苯型化合物）-----Chiral molecules

86. Chiral Nitrogen compounds

87. Homeworks