Benzene

Benzene

1. Kekule's structure

   • Alternate single and double bonds
     • FOR - This can be hydrogenated to form cyclohexane
       • C6H6+3H2 -- C6H12
     • AGAINST - Only three isomers of dichlorobenzene but kekule predicted 4
     • AGAINST - Should turn bromine water colourless as it is unsaturated but it doesn't

2. Today's benzene

   • Planar ring of 6 C's with 1.5 bonds between them and a ring of delocalized electrons above and below

3. Stability of benzene

   • Cyclohexene - cyclohexane has enthalpy change -120
     • Kekule's value should be 3 times this = -360
       • Actually -208 - a lot less
   • More stale than predicted due to the rings of delocalized electrons

4. Nitro compounds from benzene

   • Electron ring create and area of high electron density - can be attacked by nucleophlies
   • HNO3+2H2SO4 = NO2++H3O++2HSO4-
     • Made in a two step process

5. Alfred Noble

   • C6H5NH2 = TNT
     • Made through hydration of nitration

6. Aromatic ketones from benzene

   • Friedel-Crafts acylation
   • CH3COCl+AlCl3 = CH3C+0+AlCl4-