Colour by design 12.3, 12.4

Colour by design 12.3, 12.4

1. Arenes (benzene)

   • Describe what kukele's proposal was for the structure of benzene A ring of 6 carbons with 3 separate C=C bonds and 3 separate C-C bonds.
   • Benzene: C6H6, flat hexagonal shape, with a bond angle of 120
     • Areas of high electron density above and below the ring
       • Gives a very stable structure
         • undergoes reactions where the stable ring is preserved
   • Unsaturated
   • All carbon-carbon bonds are the same, the strength is between a single and a double bond
     • Means one electron from each carbon is delocalised over the whole ring.
       • Electron delocalised electron - spreading out of electrons
   • Kukule's model was rejected as the cyclic nature of the model means benzene wouldn't be as stable as it actually is
   • A benzene ring where a hydrogen has been substituted by another group - phenyl group
   • When two benzene molecules fuse together the delocalisation is spread over all the rings

2. Reactions of arenes

   • Planar molecule with areas of delocalised electron density above and below the plane
     • Attract electrophiles
       • Electrophylic substitution
   • Unlike alkenes, undergo substitution reactions, rarely addition
     • Substitution keeps the delocalised electron structure
   • Bromination
     • electrophile Br+
       • Make HBr
     • Room temperature
     • Bromine and anhydrous FeBr3
   • Chlorination
     • Electrophile Cl+
       • Make HCl
     • Room temperature
     • Chlorine + anhydrous AlCl3
   • Sulfonation
     • Conc sulfuric acid
     • Heat under reflux for hours
     • electrophile SO3
       • Make H2O
   • Nitration
     • conce nitric acid mixed with sulfuric acid
     • below 55
     • electrophile is NO2+
       • Make H2O
   • Acylation
     • Acyl chloride anhydrous AlCl3
     • heat under reflux
     • Electrophile: Positive ion formed when the Cl leaves the acyl chloride
       • Make HCl
   • Alkylation
     • Chloroalkane + anhydrous AlCl3
     • Heat under reflux
     • Electrophile positively charges ion formed after chloride leaves the alkane
       • Make HCl