Reactions of Benzene and Cyclobenzene with Bromine

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  • Comparison of reactions of Benzene and Cyclohexene with bromine
    • Benzene
      • Conditions
        • No solvent
        • Halogen Carrier catalyst (AlBr3 or FeBr3)
      • Observations
        • Br2 decolourised
        • Steamy fumes of HBr
      • Relative reactivity
        • Low reactivity
      • Type of reaction and mechanism
        • Electrophilic substitution
    • Cyclohexene
      • Conditions
        • Aqueous solution
      • Observations
        • Br2 decolourised
        • No steamy fumes
      • Relative reactivity
        • High reactivity
      • Type of reaction and mechanism
        • Electrophilic Addition
    • Reason for difference in reactivity
      • Delocalisation lowers the electron density in the pi system of benzene compared to the localised pi bond in cyclohexane
        • Consequently, electrophiles are less strongly attracted to the pi system of benzene
    • Reason for different types of reaction
      • An addition reaction replaces the pi bonding by new sigma bonds. This is favourable for the relatively weak pi bond of cyclohexane, but not for the more stable delocalised pi bonding of benzene
        • A substitution reaction in benzene allows the delocalised pi system to be retained


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