31 - HALOGENOARENE

Question 1

State the conditions and reagents needed to produce halogenoarene from arene

Answer 1

• Cl2/ Br2
• AlCl3/ AlBr3 catalyst
• benzene ring
• r.t
  > occurs via electrophilic substitution

Question 2

State the directing positions when methylbenzene reactions with Cl2 with AlCl3 catalyst (halogenation)

Answer 2

• forms two products
• 2,4 position
• 6 position when Cl2 is in excess

Question 3

Explain the difference of reactivity between halogenoalkane and halogenoarene

Answer 3

• reactivity depends on the strength of C-Cl bond
  > halogenoalkanes easily undergo nucleophilic substitution
• C-Cl bond is weak due to electronegative Cl atom
• nucleophile attacks the partially positive carbon atom
  > halogenoarene has strong C-Cl bond
• lone pairs of electrons from Cl delocalises over the benzene ring
• C-Cl have a partial double-bond character which strengthens the bond
• therefore does not readily undergo nucleophilic subs.