1. Conjugated Dienes and U.V. Spectroscopy

2. Some Dienes

3. Some Conjugated Molecules

4. Prevents DNA from Unraveling

5.  and  for Ethylene

6. Orbital Depiction of Ethylene

7. Orbital Depiction

8.  H hydrogenation

9. Carbocation is Resonance Stabilized

10. Carbocation Stability

11. Conjugate Addition of HBr

12. 1,2- vs. 1,4-Addition

13. Kinetic and Thermodynamic Products

14. Kinetic vs. Thermodynamic Control

15. 2 Different 1,4- Products Form

16. Thermodynamic Products

17. Addition to 1,3,5-Hexatriene

18. At 0 o C 1,2-addition is favored

20. At 40 o C, 1,4-addition is preferred

21. Form more stable carbocation

24. Allylic Bromination With NBS

25. Free Radical Mechanism

26. Mechanism involves the gradual generation of Br 2

27. Resonance stabilization leads to possibly several products

28. Diels-Alder Reaction a Pericyclic Reaction

30. Dienophiles Must be Electron Deficient

34. Stereochemistry

36. Bicyclic Adducts endo and exo

37. Endo Addition

38. Endo Rule

40. Identify the Diene and Dienophile that gives the Adducts

42. Two Phosphatase Inhibitors

43. A Radiosensitizer

44. Synthesis of LS-5

49. 1,3-Butadiene and Ethylene Molecular Orbitals

50. Proper Orbital Overlap

51. Overlap Must be Constructive

52. Unsymmetrical Diels-Alder Reactions

54. Lewis Acid catalysis in a Diels Alder Reaction

55. 2 o Intermediate is Preferred

56. Stereochemistry in endo Addition

57. Electrocyclic Reaction in Anti-Tumor Agent

58. Diradical Removes H atoms from Deoxyribose in Cancer Cell

59. [2+2] Cycloaddion is Forbidden

60. Photochemical [2+2] Cycloaddition Need to Irradiate

62. Suprafacial – Allowed

63. Antarafacial - Forbidden

64. [4+2] is Suprafacial, hence Allowed

66. Cycloaddition Reactions can be Planned Based on the Number of Pairs of e - ’s that Move

67. Formation of Cyclobutanes

68. A [4+6] Cycloaddition (odd # pairs of e - ’s move) Thermally Allowed

69. Retro Diels-Alder, followed by Diels-Alder

70. Intramolecular photochemical [2+2] cycloaddion

71. Ultraviolet Spectroscopy The absorption of a 171-nm photon excites an electron from the p bonding MO of ethylene to the p* antibonding MO.

72. Conjugated Dienes Absorb Energy in UV Region

73. UV Spectrum of Isoprene max = 222 nm

74. Conjugation lowers the energy differences between the HOMO and LUMO energy levels, and so conjugated dienes absorb at longer wavelengths than isolated dienes, and trienes absorb at longer wavelengths than dienes, etc. Alkyl group substitution on double bonds also causes absorption to occur at longer wavelengths.

75. HOMO-LUMO Gap lessens with increased conjugation

76. Woodward-Fieser Rules for Predicting max Double bond extending conjugation 30 nm Exocyclic double bond5 nm Alkyl group5 nm Cl, Br5 nm OH, OR6 nm SH, SR30 nm NH 2, NHR, NR 2 60 nm

77. Predict max in U.V. Spectrum

78. Determination of max