Examples of Carbocation Formation

1
Examples ofCarbocation Formation
2
Formation of Alkyl Benzene
3
Limitations ofFriedel-Crafts

• Reaction fails if benzene has a substituent that
  is more deactivating than halogen.
• Carbocations rearrange. Reaction of benzene with
  n-propyl chloride and AlCl3 produces
  isopropylbenzene.
• The alkylbenzene product is more reactive than
  benzene, so polyalkylation occurs.
  
  gt

4
Friedel-CraftsAcylation

• Acyl chloride is used in place of alkyl chloride.
• The acylium ion intermediate is resonance
  stabilized and does not rearrange like a
  carbocation.
• The product is a phenyl ketone that is less
  reactive than benzene.
  gt

5
Mechanism of Acylation
6
Clemmensen Reduction

• Acylbenzenes can be converted to alkylbenzenes by
  treatment with aqueous HCl and amalgamated zinc.

7
Gatterman-KochFormylation

• Formyl chloride is unstable. Use a high pressure
  mixture of CO, HCl, and catalyst.
• Product is benzaldehyde.

8
NucleophilicAromatic Substitution

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

9
Examples ofNucleophilic Substitution
gt
10
Addition-EliminationMechanism