Unit 3 : Reactions of Alkenes. Thermodynamics and Kinetics

1. Unit3: Reactions of Alkenes.Thermodynamics and Kinetics Hydrocarbons that contain only C-C bond are called alkanes Hydrocarbons that contain C=C bond are called alkenes or olefins (oil forming)

2. 尤加利樹油

3. 3.1 Molecular Formula and the Degree of Unsaturation Alkene CH3(CH2)nCH3 CnH2n Cyclic alkane CnH2n Cyclic alkene CnH2n-2 Alkane CH3(CH2)nCH3 CnH2n+2 Degree of unsaturation = 2 1 p bond or 1 ring, degree of unsaturation = 1

5. 3.3 The Structure of Alkenes

6. 3.4 cis-trans Isomerism Rotational barrier 63kcal/mol H3C—CH3 rotational barrier = 2.9 kcal/mol

8. Cis-Trans Interconversion in Vision

9. cis-trans Isomerism

10. 3.6 Reactivity Considerations Functional group

11. Organic Reactions • Electron-rich atoms or molecules are attracted to electron-deficient atoms or molecules • Nucleophile: an electron-rich atom or molecule • Electrophile: an electron-deficient atom or molecule • A nucleophile and an electrophile react with each other

12. Electrophiles and Nucleophiles

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14. Mechanism of the Reaction

16. 3.7 Thermodynamics and Kinetics Reaction coordinate digram

17. Thermodynamics Describes the properties of a system at equilibrium The more stable the compound, the greater its concentration at equilibrium

19. Gibbs standard free energy change This symbol indicates that the reaction takes place under standard conditions --all species at 1 M, 25 OC, and 1 atm. ↓ R is the gas constant (1.986 cal/mol OK) T is the absolute temperature (OK)

21. Free Energy, Enthalpy and Entropy DHO < 0, exothermic reaction; DHO > 0, endothermic reaction In condensed phase, DSO≈ 0. Therefore DGO ≈ DHO

22. Calculate DHO for a Certain Reaction

23. p.130

24. Solvation: the interaction between a solvent and a molecule (or ion) in solution Solvation can have a large effect on the DHO of a reaction, and it can also affect the DSO of a reaction.

25. Kinetics Deals with the rates of chemical reactions and the factors that affect those rates Free energy of activation

28. Rate Law First-order reaction Second-order reaction Second-order reaction

29. The Arrhenius equation:

30. Rate Constant and Equilibrium Constant At equlibrium, forward rate = reverse rate. k1 [A] = k-1 [B] therefore

32. Reaction Coordinate Diagram for the Addition of HBr to 2-Butene Bonds being broken pDH = 61 kcal/mol H-BrDH = 87 kcal/mol DHtotal = 148 kcal/mol Bonds being formed C-H DH = 101 kcal/mol Bonds being formed C-Br DH = 69 kcal/mol Total DH change = +47 kcal/mol Over all DH change = -22 kcal/mol

33. Reaction Coordinate Diagram for the Addition of HBr to 2-Butene -22 kcal/mol

34. 3.8 General Mechanism for Electrophilic Addition

35. 3.9 Addition of Hydrogen Halides

37. Relative Stabilities of Carbocations

39. sp3 sp2 Inductive effect

40. Relative Stabilities of Carbocations

41. 3.11 The Structure of the Transition State

42. The Hammond postulate

44. 3.12 Regioselectivity of Electrophilic Addition Reactions

45. Constitutional isomers Major product Minor product Major product Minor product Regioselective reaction Non-regioselective reaction

47. 3.13 Addition of Water and Alcohols hydration

49. Addition of Alcohol to Alkene

50. 3.14 Rearrangement of Carbocations According Markovnikov’ rule This compound should be major product