Aromatic chemistry

• How do we know when a compound contains delocalised electrons ?


  When it contains alternating single and double bonds
• when is a compound more stable ?

  Has delocalised electrons

  electrons are spread across a greater distance so it’s electron density decreases
• when you react bromine with benzene why does it not turn colourless

  Benzene has a low electron density due to its delocalised electrons

  therefore does not induce a dipole in bromine

  therefore bromine cannot act as a electrophile

  does not undergo an addition reaction
• Explain the bonding in benzene

  Each carbon forms 3 covalent bonds

  remaiming p orbitals overlap above and below the ring to form a pI system

  electrons in these p orbitals are delocalised
• explain the shape of benzene

  Benzene is planar

  bond angles are 120degrees

  c-c bonds are equal in length
• How do you for electrophile AlBr4

  Br2 + AlBr3 --> Br+ + AlBr4
• Write a reaction for the nitration of benzene

  C6H6 + HNO3 —> C6H5NO2 + H2O
• how do you form the electrophile

  HNO3 + H2SO4 —> HSO4- + H2O + NO2+