1. Isolated and Conjugated Dienes

2. Reactions of Isolated Dienes

3. The Mechanism

4. Double Bonds can have Different Reactivities

5. Reactions of Conjugated Dienes

6. 1,2-Addition and 1,4-Addition

7. Reaction of a Conjugated Diene
Mechanism for the
Reaction of a Conjugated Diene

8. The Diels–Alder Reaction forms a Six-Membered Ring

9. The Mechanism

10. Faster if there is an Electron Withdrawing Group on the Dienophile

11. The Electron Withdrawing Group makes the Electrophile a better Electrophile

12. Another Diels–Alder Reaction

13. Alkynes can also be Dienophiles
The cyclic product has two double bonds.

14. The Stereochemistry of the
Diels–Alder Reaction
The product will be a racemic mixture.

15. How to Determine the Reactants of a Diels–Alder Reaction

16. Benzene is an Aromatic Compound
The delocalization energy of benzene is 36 kcal/mol.

17. Criteria for a Compound to be Aromatic
It must have an uninterrupted cloud of π electrons.(cyclic, planar, every ring atom must have a p orbital).
The π cloud must have an odd number of pairs of π electrons.

18. Criteria for Aromaticity
Uninterrupted arrangement of p cloud
Cyclic molecule
Every atom in the ring must have a p orbital
Molecule has to be planar
Total number of p-electron pairs is odd (1,3,5…)
Exceptionally stable molecules

19. Examples of Compounds that are not Aromatic
Cyclobutadiene has an even number of pairs of π electrons.
Cyclooctatetraene has an even number of pairs of π electrons and it is not planar.

20. Nonaromatic and Aromatic Compounds
2 pairs of p electrons 2 pairs of p electrons 3 pairs of p electrons
planar nonplanar planar

21. Resonance Contributors and
the Resonance Hybrid

22. Cyclopentadienyl anion
Resonance contributors.
Overall every C atom has the same amount of negative charge
charge equally
distributed

23. Benzene
Benzene: planar, ring, all atoms have p orbitals, 3 pairs of p electrons.

24. Aromatic Compounds

26. Nomenclature of Monosubstituted Benzenes
State the name of substituent and add the word “benzene”

27. Nomenclature
Many trivial names in use

28. Nomenclature

30. How Benzene Reacts
Aromatic compounds such as benzene undergo electrophilic aromatic substitution reactions.

31. Benzene Reacts with Electrophiles
The π electrons above and below the ring make benzene a nucleophile.
Benzene attacking an electrophile is like an alkene attacking an electrophile.

32. Benzene undergoes Substitution, not Addition
Aromaticity is restored in the product from electrophilic substitution.

33. Benzene undergoes Substitution, not Addition
The reaction of benzene with an electrophile forms the aromatic substitution product, not the nonaromatic addition product.

34. An Electrophilic Aromatic Substitution Reaction
An electrophile (Y+) substitutes for H+.

35. The Mechanism for Electrophilic Aromatic Substitution

36. Generating the Electrophile:
Halogenation
Donating a lone pair to a Lewis acid weakens the Br—Br or Cl—Cl bond.

37. Halogenation of Benzene

38. Halogenation of Benzene
1st step is generating an electrophile:
FeBr3 is a Lewis acid that coordinates with Br2 and
polarizes it, generating an electrophilic Br+

39. Halogenation of Benzene

40. Generating the Electrophile:
Nitration

41. Nitration of Benzene
Nitration:

42. Nitration of Benzene
Nitration:

43. Generating the Electrophile:
Sulfonation

44. Sulfonation of Benzene

45. Sulfonation of Benzene

46. Generating the Electrophile: Friedel–Crafts Acylation and Alkylation

47. Friedel-Crafts Acylation of Benzene

48. Friedel-Crafts Acylation of Benzene

49. Friedel-Crafts Alkylation of Benzene

50. Friedel-Crafts Alkylation of Benzene

52. How Some Substituents on a Benzene Ring Can be Chemically Changed

53. How Some Substituents on a Benzene Ring Can be Chemically Changed

54. Nomenclature of Disubstituted Benzenes

57. The Effect of Substituents on Reactivity
Monosubstituted benzenes undergo electrophilic aromatic substitution.
Substituents influence reactivity.
Substituents determine position of second electrophilic substitution.
Substituents that increase electron density increase reactivity.
Substituents that decrease electron density decrease reactivity.

58. The Effect of Substituents on Reactivity

59. Donating and Withdrawing Electrons by Resonance

60. Electron-donating Substituents
Resonance contributors increase electron density in ortho
and para positions. Overall electron density is bigger.

61. Donating and Withdrawing Electrons by Resonance

62. Electron-withdrawing Substituents
Resonance contributors decrease electron density in ortho and para positions. Overall electron density is lower.

63. Substituent Effects
Both types of substituents, electron Donating and electron Withdrawing, act on the same positions, namely ortho and para, however, in opposite directions.

64. Relative Reactivity of Substituted Benzenes
Activating
Deactivating

65. Figure: UN.T1
Title:
Table The Effects of Substituents on the Reactivity of a Benzene Ring Toward Electrophilic Substitution
Caption:
Those at the top of the table are the most activating substituents when compared to hydrogen. The bottom of the table contains the deactivating groups.
Notes:
Ortho/para directors are generally activating substituents (except the halogens) while meta directors are generally deactivating substituents.

66. Classification of Substituents
Activating Substituents
(ortho/para directing):
prim. Amines
sec. Amines
tertiary amines
phenolic OH
phenol ethers
amides
phenolic esters
alkyl substituents
halides
Strongly
activating
weakly
activating
deactivating

67. Classification of Substituents
Deactivating Substituents (meta directing):
aldehydes
esters
carboxylic acid
nitrile
sulfonic acid
nitro
ammonium
weakly
deactivating
strongly
deactivating

69. The Effect of Substituents on Orientation
1. All activating substituents direct an incoming electrophile to the ortho and para positions.

70. The Effect of Substituents on Orientation
2. The weakly deactivating halogens also direct an incoming electrophile to the ortho and para positions.

71. The Effect of Substituents on Orientation
3. All moderately deactiating and strongly deactivating substituents direct an incoming electrophile to the meta position.

78. Organizing what we know about the Reactions of Organic Compounds