Chapter 4

1. Chapter 4 Reaction of Alkenes

2. Electrophilic addition to an alkene slow fast

3. Electrophilic addition of a hydrogen halide to a symmetrical alkene.

4. Electrophilic addition of a hydrogen chloride to an asymmetrical alkene.

5. Why?

6. Stabilization of a carbocation by hyperconjugation the electrons of an adjacent C-H bond spread into the empty p orbital

7. The Structure of Transition State (I) : early transition state (III) : late transition state Hammond postulate : The transition state is more similar in structure to the species to which it is more similar in energy.

8. Hammond postulate : The transition state is more similar in structure to the species to which it is more similar in energy. (I) : early transition state (III) : late transition state

9. Reaction coordinate diagram for the addition of H+to 2-methylpropene

10. In the first step of hydrohalogenation, the most stable carbocation is formed. In the second step, the halide attacks the carbocation fast.

11. Electrophilic addition to an unsymmetrical alkene Regioselectivity (자리 선택성) : selectivity due to the difference in the reactivity at reaction site to give different ratio of constitutional isomers

12. not regioselective Only product

13. Markovnikov’ rule In all electrophilic addition reaction of alkene : * the electrophile adds to the sp2 carbon that is bonded to the greater number of hydrogens . → to give more stable carbocation intermediate or * the nucleophile adds to the sp2 carbon that is bonded to the smaller number of hydrogens → nucleophile added fast to more stable carbocation

16. Addition of water to alkene there is no electrophile present to start a reaction by adding to the nucleophilic alkene Catalyzed addition of water to alkene

17. Mechanism for the electrophilic addition of water to propene H3O+ : catalyst

18. Electrophilic addition of alcohol to alkene

19. Rearrangement of a carbocation to a more stable carbocation

20. Mechanism of 1,2-hydride shift.

21. Mechanism of 1,2-alkyl shift.

22. If a rearrangement does not lead to a more stable carbocation, the rearrangement does not occur.

23. Examples of Carbocation Rearrangements

24. Addition of halogen to an alkene

25. Mechanism for the bromination of an alkene

26. Formation of cyclic bromonium ion

27. Carbocation rearrangements do not occur : because ….. Addition of HBr

28. Chlorine adds across a double bond

29. Addition of iodine is thermodynamically unfavorable

30. Formation of halohydrins

31. Transition state of halohydrin formation

32. Effect of the added nucleophiles Excess nucleophiles Na+ or K+ cannot form covalent bonds

33. Oxymercuration - Reduction.

35. Epoxidation of an alkene with peroxyacids R = CH3, peroxyacetic acid = C6H5, peroxybenzoic acid

36. Mechanism for the epoxidation of an alkene similar mechanism

37. Nomenclature of epoxides

38. Reaction of a Carbene with alkenes empty p orbital Carbene = Carbocation + Carbanion

39. Hydroboration-oxidation of an alkene

40. Acid-catalyzed addition of water vs. hydroboration-oxidation

41. Borane-tetrahydrofuran complex : Lewis Acid-Base complex

42. Mechanism of the addition of borane to an alkene Addition of BH3 vs. addition of HBr to an alkene

43. Formation of a dialkylborane and trialkylborane

44. Oxidation of the trialkylborane

45. Example of hydroboration-oxidation

46. Catalytic hydrogenation of alkenes

47. Catalytic hydrogenation of an alkene : Mechanism

48. Heat of hydrogenation of various alkenes.

49. The relative energies of three isomeric alkenes 127 kJ/mol 119 kJ/mol 113 kJ/mol relative stabilities

50. Relative stabilities of substituted alkenes