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

L27. TOPIC 8. ADDITIONS TO ALKENES AND ALKYNES (Chapter 8 and parts of chapters 7, 10 and 11). OBJECTIVES. 1. Describe mechanisms for addition reactions of alkenes and alkynes Predict the structure of the product(s) of addition reactions

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

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  1. L27 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, aelimination and addition chemistry to propose synthetic routes to useful value-added compounds

  3. PREVIEW OF REACTIVITY Alkenes and Alkynes are Weakly Basic and Weakly Nucleophilic S:8.1

  4. HYDROGENATION OF ALKENESAND ALKYNES S:7.13,14 Prob:7.40,41,43-45;8.30,38 Hydrogenation of Alkenes

  5. Soybean Oil Mixture of saturated and various cis-unsaturated hydrocarbon chains. Low melting (-16 °C) because cis C=C impede crystallization. • A Practical Application of Hydrogenation – HydrogenatedOils and Fats http://www.fb.com/nefb/ag-ed/soybean.gif Margarine Mixture of saturated hydrocarbon chains (some C=C kept to adjust consistency). Saturated alkyl chains pack together (crystallize). http://www.nicssa.co.uk/Contentpages/Fitness&Exercise/contentweightetc.htm http://www.bassriverchairs.com/new_prodMargarine.html

  6. Hydrogenation of Alkynes Complete Hydrogenation cis-Semihydrogenation S:7.15

  7. Dissolving Metal Reduction

  8. ADDITION OF HYDROGEN HALIDESTO ALKENES AND ALKYNES S:8.2 Prob:8.29,33 • Overview

  9. Addition of H-Hal to Alkenes • Mechanism

  10. 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.

  11. 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.

  12. Stereochemistry of H–Hal Addition to Alkenes S:8.3

  13. Anti-Markovnikov Addition of H-Hal to Alkenes Mechanistic Rationale for Anti-Markovnikov Addition S:10.9

  14. Addition of H-Hal to Alkynes S:8.13

  15. L28 SYNTHESIS OF ALCOHOLSBY HYDRATION OF ALKENES S:8.5 Addition of Water to Alkenes

  16. Problem: Acid Catalyzed Hydration of Alkenes • Intermediate carbocations can rearrange.

  17. S11.4-7Prob:11.33,35(c-e),40,46 • Solution: Oxymercuration-Demercuration • e.g., • Step 1: Oxymercuration • Step 2: Demercuration

  18. Mechanism

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

  20. Mechanism: Regiochemistry

  21. Stereochemistry

  22. Hydration of Alkynes

  23. A REVIEW OF REACTIONS We have seen hydrogenation, hydration and addition of HBr to alkenes. But there are some other important addition reactions…

  24. SYNTHETIC STRATEGIES S:4.20 Prob:7.24,27 Problem: Synthesize 1-R-cyano-2-R-methylcyclohexane (shown below) using any starting material.

  25. 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.

  26. L29 ADDITION OF BROMINE AND CHLORINETO ALKENES AND ALKYNES S:8.6 Prob:8.41 • Overview

  27. S:8.7 • Addition of Hal2 to Alkenes • Stereochemistry

  28. Mechanism

  29. S:8.8 • Formation of Halohydrins

  30. Mechanism

  31. L30 S:8.12, 16.5B Addition of Hal2 to Alkynes

  32. ADDITION OF CARBENES TO ALKENES S:8.9 • What is a Carbene? • What is a Carbenoid?

  33. Example Additions • Mechanism

  34. EPOXIDES S11.17Prob 11.38 Synthesis MMPP mCPBA

  35. S11.18-19Prob 11.38 • Nucleophilic Ring-opening Stereochemistry

  36. Regiochemistry

  37. Addition of Other Nucleophiles Problem: Why is it important to use an excess of amine in the last example?

  38. OXIDATION OF ALKENESAND ALKYNES S:8.10 Prob:8.27,31,32,35,39,40,46,47 syn Hydroxylation of Alkenes

  39. Oxidative Cleavage of Alkenes Permanganate Oxidation S:8.11

  40. Ozonolysis Problem: What is the structure of compound A in the following scheme? A

  41. 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? S:8.14

  42. 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) S:10.10

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

  44. Common Chain-Growth Polymers

  45. L31 SYNTHETIC STRATEGIES S:8.15 (also see 4.20) Prob:8.21-26,37 • Add to your chart of organic reactions • No more reactions! For now!!!

  46. DESIGNING SYNTHESES One 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?

  47. 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?

  48. Problem: Solomons 8.25(b). Show how 1-butyne could be synthesized from each of the following: (b) 1-chlorobutane

  49. Problem:

  50. Problem:

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