aromatic chemistry

• structure of benzene

  -each C atom forms sigma bond using 2p2 orbital

  -remaining p orbitals overlap with p orbitals of neighbouring C atoms to form pi system

  -sideways overlap of p orbitals results in e- being delocalised and able to freely spread over entire ring cause pi system

  -regular, planar 120

  -C-C bonds are equal
• reactions of benzene - why are reagents needed

  -delocalised pi system is extremely stable and a region of high e- density

  -electrophiles cannot simple be added

  -electrophile has to be produced in situ, by adding appropriate reagent to reaction mixture
• nitration of benzene - formation of electrophile

  2H2SO4 + HNO3 <-----> NO2+ + 2HSO4- + H3O+
• nitration of benzene : reforming the catalyst

  HSO4- + H+ ----> H2SO4
• stability of benzene

  -stable due to delocalised ring of electrons

  -C-C bonds are neither single nor double, instead an intermediate length with e- in p orbital sticking above and below the carbon ring
• Friedel-Crafts Acylation - generating the electrophile

  acyl chloride --AlCl3--> carbocation + AlCl4-

  eg.

  CH3COCl + AlCl3 -----> CH3CO+ + AlCl4-
• reactions of arenes: nitration

  conditions - mixture of conc. HNO3 and conc. H2SO4 temp from 25-60 degrees

  products - nitroarene
• reactions of arenes: Friedel-crafts acylation

  conditions - acyl chloride and anhydrous AlCl3 cat.

  products - acylbenzene
• reactions of arenes: complete oxidation

  conditions - hot alkaline KMnO4 and then dilute acid

  products - benzoic acid
• reactions of arenes: hydrogenation

  conditions - hydrogen gas and Pt/Ni cat. and heat

  products - cyclohexane