aromatic compounds

• how many sigma bonds make up a benzene?


  12
• how many pi bonds make up a benzene?


  3
• what is the molecular formula of benzene?


  C6H6
• Describe the structure of benzene?


  Planar molecule, C bond angles are 120 degrees, C-C bond lengths are equal
• When drawing the delocalised pi bonding of benzene, what labels are required?


  p-orbitals, p-orbital overlap above and below the plane of the molecule, pi bond
• State the 1st evidence that supports the delocalisation model of benzene 


  C-C bond lengths equal due to delocalised pi bonds
• State the 2nd evidence that supports the delocalisation model of benzene 


  Enthalpy of hydrogenation of benzene is less endothermic than expected. Delocalised pi-ring makes it more stable
• In the enthalpy of hydrogenation of benzene, how does the actual enthalpy compare to the expected enthalpy of Kekule's model?


  Kekule = -360KJmol-1

  Delocalised model = -208KJmol-1

  Delocalised model is 152KJmol-1 more stable
• State the third evidence that supports the delocalisation model of benzene


  Benzene does not undergo electrophilic addition reactions. e.g with Br2

  A catalyst is needed and it undergoes electrophilic addition instead
• Name C6H5Cl

  Chlorobenzene
• Name C6H5CH3

  Methylbenzene
• Name C6H5COOH

  Benzene carboxylic acid
• What new functional group is substituted onto Benzene in nitration?


  -NO2
• Name a benzene molecule with a nitro group attached

  Nitrobenzene
• Write an overall equation for the nitration of benzene

  C6H6 + HNO3 -> C6H5NO2 + H20
• Give the reagents and conditions required in nitration of benzene


  Concentrated HNO3 and concentrated H2SO4 catalyst
• What is the electrophile used in the nitration of benzene? 


  NO2+
• Write an equation for the formation of the electrophile in nitration of benzene


  HNO3 + H2SO4 -> NO2+ + HSO4- + H+
• Name the mechanism in the nitration of benzene


  Electrophilic substitution
• Explain the first step in the nitration of benzene mechanism


  A pair of electrons forms a bind to the NO2+
• Describe the intermediate formed in the second step of the nitration of benzene mechanism

  A benzene with a partial ring and positive charge that doesn't go beyond the carbons either side of the C with NO2 attached but does extend beyond the carbons at the back of the molecule
• Describe the second step in the nitration if benzene mechanism


  The electron pair from the C-H bond breaks to complete the partial benzene ring
• write the equation for the reformation of the catalyst in nitration of benzene


  HSO4- + H+ -> H2SO4
• When drawing electrophilic substitution mechanisms, what do you need to be careful to check in the intermediate?


  Compare the products to the intermediate to ensure the electrophile is on the correct C atom
• State two uses of nitrobenzene


  Explosives and dyes