F324- Rings, Polymers & Analysis

F324- Rings, Polymers & Analysis

1. BENZENE

   • Why does benzene follow the delocalised model & not the Kekule' structure?
     • 1- Bond Length: The bond length of a single bond is longer than a double bond, however in benzene all the bond lengths are equal due to the delocalised electrons distributed around the whole structure
       • 2- Kekule suggested the benzene reacts in a similar way to alkenes but under normal conditions benzene doesn't decolourise bromine water. Also benzene undergoes substitution reactions and not addition
         • 3- the enthalpy change of hydrogenation is more stable in benzene than alkenes due to the delocalised electron ring distributed around the whole structure
   • Reactions of benzene:

2. PHENOL

   • Why does phenol react more readily than benzene?
     • 1- In phenol electron density increases (oxygen)
       • 2- The electrophile attacking Phenol becomes polarised (due to oxygen)
         • 3- The delocalised electron ring also pulls the oxygen electrons into the delocalised electron cloud
           • 4- Phenols undergo substitution reactions easier due to the lone pair on the oxygen
   • Reactions of phenols
   • uses of phenols:
     • Production of plastics, antiseptics, disinfectants, resins for paints & varnishes.

3. Carbonyl's

   • Aldehydes are prepared from the distillation (oxidation) of primary alcohols using acidified potassium dichromate.
   • testing for Primary, secondary and tertiary alcohols: using acidified potassium dichromate: the color change should be from orange to green

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