1. L26
TOPIC 8. ADDITIONS TO ALKENES AND ALKYNES (Chapter 8 and parts of chapters 7, 10 and 11)

2. OBJECTIVES
1. Describe mechanisms for addition reactions of alkenes and alkynes
Predict the structure of the product(s) of addition reactions
Understand the mechanisms which explain the regiochemical and stereochemical outcome of addition reactions
Use combination of substitution, elimination and addition chemistry to propose synthetic routes to useful value-added compounds

3. HYDROGENATION OF ALKENES AND ALKYNES
Prob: ; 8.30e,g-i,37,45
Hydrogenation of Alkenes

4. A Practical Application of Hydrogenation – Hydrogenated Oils and Fats
Soybean Oil
Mixture of saturated and various cis-unsaturated hydrocarbon chains.
Low melting (-16 °C) because cis C=C impede crystallization.
Margarine
Mixture of saturated hydrocarbon chains (some C=C kept to adjust consistency). Saturated alkyl chains pack together (crystallize).

5. Hydrogenation of Alkynes
Complete Hydrogenation
cis-Semihydrogenation

6. Dissolving Metal Reduction

7. PRS PREVIEW OF REACTIVITY
Alkenes and Alkynes are Weakly _____ and Weakly _____________
S:8.1
PRS

8. PRS
Which of the following mechanistic steps is most likely to occur? 1 2 3 4
PRS

9. ADDITION OF HYDROGEN HALIDES TO ALKENES AND ALKYNES
Prob: 8.27(28) a,b,f,j, 29b-g,35
Overview

10. Addition of H-Hal to Alkenes
Mechanism

11. PRS Regiochemistry Markovnikov’s Rule
In the addition of HX to an unsymmetrical alkene, the hydrogen adds to the
_____________ substituted carbon and the X groups adds to the
_____________ substituted carbon.
PRS

12. PRS
Which of the following cannot be made by Markovnikov addition of HBr to an appropriate alkene? 1 2 3 4
PRS

13. PRS The Basis of Markovnikov’s Rule: Stability of Carbocations
The more substituted carbocation is formed. Remember hyperconjugation!
Mechanistic Restatement of Markovnikov’s Rule
In the ionic addition of HX to an unsymmetrical alkene, protonation gives the more stable carbocation as an intermediate.

14. PRS
Which of the following is the most stable carbocation? 1 2 3 4
PRS

15. Stereochemistry of H–Hal Addition to Alkenes

16. PRS Anti-Markovnikov Addition of H-Hal to Alkenes
Mechanistic Rationale for Anti-Markovnikov Addition
PRS

17. PRS
Which of the following radicals is more stable? 1 2
PRS

18. Addition of H-Hal to Alkynes
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19. HWeb
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20. SYNTHESIS OF ALCOHOLS BY HYDRATION OF ALKENES
Prob: 8.27(28)c,32, 58, (a-g),38a,d, 39,46,48
Addition of Water to Alkenes
PRS

21. PRS
Which of the following mechanistic steps is most likely to occur? 1 2
PRS

22. Proceeds via Markovnikov addition
PRS

23. PRS
Which of the following cannot be made by Markovnikov hydration of an appropriate alkene? 1 2 3 4
PRS

24. Rearrangements During Acid Catalyzed Hydration of Alkenes
Intermediate carbocations can rearrange.

25. Oxymercuration-Demercuration of Alkenes
e.g.,
Step 1: Oxymercuration
Step 2: Demercuration

26. Mechanism
PRS

27. PRS
Which of the following cannot be made in high yield by oxymercuration-demercuration of an appropriate alkene? 1 2 3 4
PRS

28. Hydroboration-Oxidation: Anti-Markovnikov Hydration of Alkenes
e.g.,
Step 1: Hydroboration
Step 2: Oxidation

29. Mechanism: Regiochemistry

30. Stereochemistry
PRS

31. PRS
Which of the following can be made by hydroboration-oxidation of an appropriate alkene?
1 only A
2 only B
3 only B and C
4 only B and D
PRS

32. Hydration of Alkynes (covered in 16.5B)

33. SYNTHETIC STRATEGIES
Prob:7.24
Problem: Synthesize cis-1-cyano-2-methylcyclohexane (shown below) using any hydrocarbon.

34. Problem: Female houseflies attract males with a pheromone which has been shown to be Z-9-tricosene (C23H46). Synthesize this compound starting with organic compounds containing 13 or less carbon atoms.
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35. HWeb
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36. ADDITION OF BROMINE AND CHLORINE TO ALKENES AND ALKYNES
Prob: 8.30c,d,31,54
Overview

37. Addition of Hal2 to Alkenes
Stereochemistry
PRS
PRS

38. PRS
What is the relationship between the following pair of compounds?
1 identical
2 enantiomers
3 diasteromers
4 consitutional isomers
PRS

39. PRS
What is the relationship between the following pair of compounds?
1 identical
2 enantiomers
3 diasteromers
4 consitutional isomers
PRS

40. Mechanism

41. Formation of Halohydrins

42. Mechanism
PRS

43. PRS
Which of the following bromohydrins can be prepared from an appropriate alkene?
1 2
3 4
PRS

44. Addition of Hal2 to Alkynes
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45. HWeb
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46. ADDITION OF CARBENES TO ALKENES
What is a Carbene?
What is a Carbenoid?
PRS

47. PRS
How many electrons does the carbon atom of methylene (carbene) have in its valance shell, what is the formal charge?
:CH2
1 4, +2
2 4, 0
3 6, +2
4 6, 0
5 6, -1
6 8, -1
PRS

48. Additions to Alkenes
Mechanism

49. EPOXIDES S:
Synthesis
Prob 11.43,44
MMPP
mCPBA

50. Nucleophilic Ring-opening
Stereochemistry

51. Regiochemistry

52. Addition of Other Nucleophiles
PRS

53. PRS
What is the major organic product of the following sequence of reactions?
PRS

54. OXIDATION OF ALKENES AND ALKYNES
Prob: 8.27(28)k-n, 30j,k,46,47
Syn-Hydroxylation of Alkenes

55. Oxidative Cleavage of Alkenes
Permanganate Oxidation

56. Ozonolysis
PRS

57. PRS PRS What is the structure of compound A in the following scheme?
PRS

58. HWeb Oxidative Cleavage of Alkynes
Problem: Compound X (C10H18) gave pentanoic acid upon reaction with basic potassium permanganate followed by acidification. What is the structure of compound X?
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59. HWeb
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60. RADICAL POLYMERIZATION OF ALKENES (CHAIN-GROWTH POLYMERS)
About 60 x 109 pounds of ethylene are manufactured and used each year, primarily to make polyethylene
Roll of Radical Initiator (Chain Initiation)
L30
S:10.10

61. Chain-Growth (Chain Propagation)
End of Growth (Chain Termination)

62. Common Chain-Growth Polymers

63. SYNTHETIC STRATEGIES Add to your chart of organic reactions
Prob: ,44
Add to your chart of organic reactions
No more reactions! For now!!!

64. DESIGNING SYNTHESES One Step Syntheses Two Step Syntheses
This is just the opposite of learning reactions - just think backwards. Although one step syntheses are relatively easy, they are harder than learning reactions.
Two Step Syntheses
This is involves considerable imagination and is quite different than “just the opposite of learning reactions”. You must be able to conceive of the intermediate. However, there is a direct link between the intermediate and both the product and the starting material. Think “retro” (retrosynthesis) - how do you synthesize the product from anything? Can you then synthesize your proposed synthetic intermediate from the starting material?

65. Three Step Syntheses
Three design of three-step organic syntheses requires a little more imagination and can be a little more difficult than two-step syntheses. You must be able to conceive of two intermediates. In this case there may not be a clear link between intermediate one and the product or intermediate two and the starting material. Again “think retro”. Can you think of ANY compounds that could be converted to the product by chemistry you know? Can you then think of one or more compounds that could be converted to these proposed intermediates by chemistry you know? Can any of these second proposed intermediates be synthesized from the starting material?

66. Problem: Solomons 8.31(b). Show how 1-butyne could be synthesized from each of the following: (b) 1-chlorobutane

67. Problem:

68. Problem:

69. Problem:

70. Problem: Propose a synthesis of 1-methyl-1,2-cyclopentanediol (with the two hydroxy groups trans to one another) from methylcyclopentane.
Prob: ,35, 37,38,46

71. Problem: An insect physiologist required 4Z-hexen-2-ol for the study of insect pheromones. Propose a synthesis of 4Z-hexen-2-ol from propene.

72. HWeb TOPIC 8 ON EXAM 4 Types of Questions
- Describe addition reaction mechanisms
- Predict the products of addition reactions
The problems in the book are good examples of the types of problems on the exam.
Preparing for Exam 4:
- Work as many problems as possible.
- Work in groups.
- Do the “Learning Group Problem” at the end of the chapter.
- Work through the practice exam
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73. HWeb
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