1. Conjugated Dienes and U.V. Spectroscopy

2. Some Dienes

3. Some Conjugated Molecules

4. Prevents DNA from Unraveling

5. Orbital Depiction of Ethylene

6. Orbital Depiction

7. DHhydrogenation

8. Carbocation is Resonance Stabilized

9. Carbocation Stability

10. Conjugate Addition of HBr

11. 1,2- vs. 1,4-Addition

12. Kinetic and Thermodynamic Products

13. Kinetic vs. Thermodynamic Control

14. 2 Different 1,4- Products Form

15. Thermodynamic Products

16. Addition to 1,3,5-Hexatriene

17. At 0oC 1,2-addition is favored

19. At 40oC, 1,4-addition is preferred

20. Form more stable carbocation

23. Allylic Bromination With NBS

24. Free Radical Mechanism

25. Mechanism involves the gradual generation of Br2

26. Resonance stabilization leads to possibly several products

27. Diels-Alder Reaction a Pericyclic Reaction

29. Dienophiles Must be Electron Deficient

33. Stereochemistry

35. Bicyclic Adducts endo and exo

36. Endo Addition

38. Identify the Diene and Dienophile that gives the Adducts

40. Two Phosphatase Inhibitors

41. A Radiosensitizer

42. Synthesis of LS-5

47. 1,3-Butadiene and Ethylene Molecular Orbitals

48. Proper Orbital Overlap

49. Overlap Must be Constructive

50. Unsymmetrical Diels-Alder Reactions

52. Lewis Acid catalysis in a Diels Alder Reaction

53. 2o Intermediate is Preferred

54. Stereochemistry in endo Addition

55. Electrocyclic Reaction in Anti-Tumor Agent

56. Diradical Removes H atoms from Deoxyribose in Cancer Cell

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

59. Suprafacial – Allowed

60. Antarafacial - Forbidden

61. [4+2] is Suprafacial, hence Allowed

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

64. Formation of Cyclobutanes

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

66. Intramolecular photochemical [2+2] cycloaddion

67. Adjacent Thymines (T’s) in DNA
Susceptible to [2+2] cycloaddition in sunlight (UV-B, nm)

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

69. Conjugated Dienes Absorb Energy in UV Region

70. UV Spectrum of Isoprene lmax = 222 nm

71. 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.

72. HOMO-LUMO Gap lessens with increased conjugation

73. Woodward-Fieser Rules for Predicting lmax
Double bond extending conjugation
30 nm
Exocyclic double bond
5 nm
Alkyl group
Cl, Br
OH, OR
6 nm
SH, SR
NH2, NHR, NR2
60 nm

74. Predict lmax in U.V. Spectrum

75. Determination of lmax

76. Determination of lmax

77. Determination of lmax