1. Alkenes and alkynes (II)
9.1 Introduction: Additions to alkenes
We shall study other examples of additions to the double bonds of alkenes. We begin with the additions of hydrogen halides, sulfuric acid, water (in the presence of an acid catalyst), and halogens.

2. An Addition reaction

3. 1. An addition reaction results in the conversion of one pi π -bond and one sigma-bond into two sigma bonds

4. 2. The electrons of the pi-bond are exposed
2. The electrons of the pi-bond are exposed. Because the pi-bond results from overlapping p orbital, the pi electrons lie above and below the plane of the double bond:

5. Hydrogen halides react with alkenes

6. 9.2 Addition of Hydrogen Halides to Alkenes: Markovnikov’s Rule (马氏规则）
What is it Mar’s Rule?-----The addition of HX to an alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms.

7. Markovnikov’s Rule (马氏规则）

9. A mechanism for addition of a hydrogen halide to an alkene (two steps;)

10. 9.2A Theoretical explanation of Markovnikov’s Rule
1. Electronic Effects (电子效应）

12. 2. The Stabilities of carbocation （碳阳离子的稳定性解释马氏规则）

13. The Stabilities of carbocation

14. Mar’s Rule help us to predict the outcome of the addition reaction

15. 9.2D An exception to Markovnikov’s Rule (马氏规则例外）
The addition of HBr to alkenes, it is Only when HBr is used in the presence of peroxides (ROOR), it is an exception to Mar’ Rule.

16. 9.3 Stereochemistry of the Ionic Addition to an alkene
We got a racemic form? Do you know why?

18. 9.4 Addition of sulfuric acid to alkenes

19. The addition of sulfuric acid is also regioselective (区域选择性）

20. 9.4A Alcohol from alkyl hydrogen sulfates (从硫酸氢乙酯制醇）
Alkyl hydrogen sulfates can be easily hydrolyzed to alcohols by heating them with water

21. 9.5 Addition of water to alkenes: Acid-catalyzed hydration
The acid-catalyzed addition of water to the double bond of an alkene is a method for the preparation of low molecular weight alcohols

22. An example is the hydration of 2-methylpropene

23. Mechanism for the hydration of 2-methylpropene

25. Alkenes hydration is followed the occurrence of rearrangements

26. 9.6 Addition of bromine and chlorine to alkenes
1. Alkanes react with bromine

27. 2. Addition of bromine and chlorine to alkenes

28. Distinguish alkanes with alkenes（区别烷烃和烯烃）

29. Distinguish cycloalkanes with cycloalkenes（区别环烷烃和环烯烃）

30. 3. Addition reaction of chlorine to alkenes

31. 9.6A Mechanism of halogen addition

32. 9.7 Stereochemistry of the addition of halogens to alkenes
It is anti addition (反式加成）

33. This anti addition of bromine to cyclopentene can be explained by a mechanism

34. Most stable
conformation

35. 9.7A Stereospecific reactions （立体专一性反应）
trans-2-Butene reacts with bromine

36. Cis-2-Butene reacts with bromine

37. 9.8 Halohydrin formation （卤代醇的形成）
If the halogenation of an alkene is carried out in aqueous solution (rather than in carbon tetrachloride), the major product of the overall reaction is not a vic-dihalide, but rather it is a halo alcohol called a halohydrin.

38. Halohydrin formation can be explained by the following mechanism:

39. Isobutene reacts with bromine in water

40. 9.9 Radical addition to alkenes: The anti-Markovnikov addition of hydrogen bromide

42. Free Radical reaction

43. 9.9A Other radical additions to alkenes
Tetrabromomethane (CBr4) reacts with 1-octene(1-辛烯)to yield 1,1,1,3-tetrabromononane

44. The mechanism for this reaction is as follows:

45. Other examples of radical additions to alkenes are the following:

46. 9.10 Radical polymerization of alkenes (烯烃的自由基聚合）:
Addition polymers (加成聚合）

47. Other common addition polymers

49. 9.11 Oxidations of alkenes (烯烃的氧化）: Syn hydroxylation （顺式-羟基化作用）
Alkenes undergo a number of reactions in which the carbon-carbon double bond is oxidized. Potassium permanganate (KMnO4) or osmiun tetroxide （OsO4), for example, can be used to oxidize alkenes to 1,2-diols (1,2-二醇） called glycols （乙二醇）.

51. 9.11A Syn hydroxylation of alkenes----Mechanism

52. However, osmium tetroxide is highly toxic and is very expensive.

53. 9.12 Oxidative cleavage of alkenes
Alkenes are oxidatively cleaved to salts of carboxylic acids by hot permanganate solutions.

54. An unknown alkene with the formula C7H12 undergoes oxidation by hot basic KMnO4 to yield, after acidification, only one product:

55. 9.12A Ozonolysis of alkenes (烯烃的臭O3氧化）

56. The overall process of ozonolysis followed by reduction with zinc and water amounts to a disconnection of the carbon-carbon double bond in the following fashion.

58. 9.14 Addition of bromine and chlorine to alkynes

59. It is usually possible to prepare a dihaloalkene by simply adding one molar equivalent of the halogen

60. 9.15 Addition of hydrogen halides to alkynes (炔烃与卤化氢的加成）

62. 9.19A Chemical tests 9.19B Concentrated sulfuric acid (H2SO4)
9.19 Simple chemical tests for alkanes, alkenes, alkynes, alkyl halides, and alcohols
9.19A Chemical tests
9.19B Concentrated sulfuric acid (H2SO4)

63. 9.19C Bromine in carbon tetrachloride ) (Br2/CCl4)

64. 9.19D Cold dilute potassium permanganate (KMnO4)

65. 9.19E Alcoholic silver nitrate (AgNO3 / ROH)

66. 9.19F Silver Nitrate in ammonia (AgNO3 / NH3)

67. Special Topic C-----Divalent carbon compounds: Carbenes (卡宾 or 碳烯）
Neutral divalent carbon compounds are called carbenes (卡宾 CH2: Methylene）
Most carbenes are highly unstable compounds.
The reactions show a stereospecificity
The reactions of carbenes are also of great synthetic use

68. C.1 Structure of methylene (carbenes)
1. The preparation of carbenes

69. C.2 Reactions of Methylene
Methylene reacts with alkenes by adding to the double bond to form cyclopropanes