aromatic

• delocalisation (arenes)


  the pi electrons are spread over several atoms
• how many electrons are present in a benzene molecules?

  30 e-

  6 C-H = 12e- (sigma)

  3 C=C = 6e- + 6e- (sigma and pi)

  3 C-C = 6e- (sigma)
• reaction that benzene molecules undergo

  electrophilic substitution
• evidence proving delocalised benzene structure

  carbon carbon bonds all same length (intermediate between C-C and C=C)

  cyclohexene is hydrogenated, the enthalpy change for adding hydrogen across 1 double bond is -120kJ/mol.

  benzene has 3 double bonds, it should have an enthalpy change of -360kJ/mol (3x120).

   However, when benzene is hydrogenated, it releases -208kJ/mol, showing it to be more stable than Kekulé's
• why does benzene react by substitution while alkenes by addition

  substitution reactions maintain the stability of the ring (would be lost in addition) and require a catalyst

  e- in alkene less stable and more readily available and reacts spontaneously
• what colour is methyl 3-nitrobenzoate

  cream solid

  
• why is the nitrating mixture added to methyl benzoate below 10degrees

  prevent multiple nitrations which would form an explosive compound
• 2 fused benzene rings

  naphthalene

  C10H8
• 3 fused benzene rings

  anthracene

  C14H10