Topic 10 Aromatic chem

• What is the formula of Benzene? [1]

  C6H6
• What is the structure of Benzene? [1]

  PLamar cyclic
• For benzene each carbon atom forms single covalent bonds to the carbon on either side of it and one hydrogen atom
• For benzene the spare electrons form a ring of delocalised electrons
• Talk about the stability of benzene [4]

  Cyclohexene has one double bond. when it is hydrogenated, the Enthalpy change is -120kjmol-1. If benzene had three double bonds you’d expect it to have an Enthalpy of hydrogenation of -360kjmol-1

  the experimental Enthalpy is -208 so less exothermic than expected

  energy is put in to break bonds and released when bonds are made. So more must have been put in to break the bonds in benzene than would be needed to break the bonds in the theoretical 3 double bonded one

  The difference indicates that benzene is more stable due to the delocalised electrons
• Why does benzene undergo electrophilic substitution but not electrophilic addition? [2]

  Benzene ring is made up of high electron density so attracts electrophilic. Benzene ring is stable so doesnt undergo electro add which would destroy delocalised ring. Instead undergoes electro sub where one of the hydrogens is subbed for an electrophile
• What catalyst does friedel-crafts Acyl action use? [1]

  Uses catalyst-halogen carrier
• Look at notes for acylation mechanism
• For fried crafts of benzene- reactants need to be hated under refulx in a non aqueous solvent for the reaction to occur
• What are the conditions for the nitration of benzene? [2]

  Warm benzene with concentrated nitric acid and concentrated sulfuric acid you get nitrobenzene
• What is the catalyst used in the nitration of benzene? [1]

  Sulfuric acid acts as a catalyst
• What is the equation for the nitration of benzene? [1]

  HNO3 + H2SO4 -> H2NO3+ +HSO4^- -> H2NO3^+ -> NO2^+ +H2O
• What is mononitration?[1]

  One NO2 group added
• What temperature is needed for the mononitartion of benzene? [1]

  below 55 degrees