The acylium ion can act as the electrophile in the acylation reaction. It is stabilized by resonance.

1
(No Transcript)
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
(No Transcript)
6
The acylium ion can act as the electrophile in
the acylation reaction. It is stabilized by
resonance.
7
Not done yet though!!!
8
(No Transcript)
9
When forming the carbocation electrophile, it can
undergo standard stabilization rearrangements
10
(No Transcript)
11
(No Transcript)
12
3)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
NucleophilicAromatic Substitution

• A nucleophile replaces a leaving group on the
  aromatic ring.
• Electron-withdrawing substituents activate the
  ring for nucleophilic substitution.
  
  gt

18
Examples ofNucleophilic Substitution
gt
19
Addition-Elimination Mechanism
20
Benzyne Mechanism

• Reactant is halobenzene with no
  electron-withdrawing groups on the ring.
• Use a very strong base like NaNH2.
  
  
  
  gt

21
Benzyne Intermediate
22
Chlorination of Benzene

• Addition to the benzene ring may occur with high
  heat and pressure (or light).
• The first Cl2 addition is difficult, but the next
  2 moles add rapidly.
• The product, benzene hexachloride, is an
  insecticide.

23
Catalytic Hydrogenation

• Elevated heat and pressure is required.
• Possible catalysts Pt, Pd, Ni, Ru, Rh.
• Reduction cannot be stopped at an intermediate
  stage.

24
Birch Reduction Regiospecific

• A carbon with an e--withdrawing group
• is reduced.

• A carbon with an e--releasing group
• is not reduced.

25
Birch Mechanism
26
Side-Chain Oxidation

• Alkylbenzenes are oxidized to benzoic acid by hot
  KMnO4 or Na2Cr2O7/H2SO4.

27
Side-Chain Halogenation

• Benzylic position is the most reactive.
• Chlorination is not as selective as bromination,
  results in mixtures.
• Br2 reacts only at the benzylic position.

28
SN1 Reactions

• Benzylic carbocations are resonance-stabilized,
  easily formed.
• Benzyl halides undergo SN1 reactions.

29
SN2 Reactions

• Benzylic halides are 100 times more reactive than
  primary halides via SN2.
• Transition state is stabilized by ring.

30
Reactions of Phenols

• Some reactions like aliphatic alcohols
• phenol carboxylic acid ? ester
• phenol aq. NaOH ? phenoxide ion
• Oxidation to quinones 1,4-diketones.

31
Quinones

• Hydroquinone is used as a developer for film. It
  reacts with light-sensitized AgBr grains,
  converting it to black Ag.
• Coenzyme Q is an oxidizing agent found in the
  mitochondria of cells.
  gt

32
ElectrophilicSubstitution of Phenols

• Phenols and phenoxides are highly reactive.
• Only a weak catalyst (HF) required for
  Friedel-Crafts reaction.
• Tribromination occurs without catalyst.
• Even reacts with CO2.

33
End of Chapter 17