Aromatic Chemistry

A mindmap of all you need to know for aromatic chemistry A2.

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  • Created by: Phoebe
  • Created on: 17-12-12 20:26
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  • Aromatic Chemistry
    • Benzene
      • Structure
        • Originally thought to contain alternate single and double bonds
          • Kekule Structure
          • Double bonds are shorter than single bonds
          • All 6 C-C bonds have the same length
          • All 6 bonded electrons are delocalised
          • The molecule is planar
          • Any molecule containing the benzene ring is aromatic
      • Stability
        • The delocalization of the electrons in benzene makes the molecule more stable than expected for a molecule with three double bonds
        • The enthalpy of hydrogenation of benzene is significantly less than three times the enthalpy of hydrogenation of a typical alkene. This is good evidence that delocalization confers stability to the molecule
      • Reactions
        • It will not undergo addition reactions
          • Delocalised system is stable
        • It undergoes substitution reactions
          • The delocalized electrons are an electron-rich area, and they are thus susceptible to attack by electrophiles
        • Nitration
          • H2SO4 + HNO3 <=> H2NO3+         + HSO4-      H2NO3+ --> H2O + NO2+
          • C6H6 + HNO3 --> C6H5NO2 + H2O
            • Product = nitrobenzene
          • sulphuric acid behaves as a catalyst
        • Alkylation
          • Haloalkanes
            • Benzene reacts with chloroalkanes in the presence of anhydrous AlCl3 under reflux at 50oC to form alkylbenzenes
            • R-Cl + AlCl3   -->  R+  + AlCl4-
              • AlCl3 acts as a catalyst
            • C6H6 + RCl   --> C6H5R + HCl
          • Alkenes
            • benzene with alkenes in the presence of HCl and AlCl3, under reflux at temperatures below 50oC
              • AlCl3 and the HCl act as catalysts
            • C6H6 + R1R2C=CR3R4 --> C6H5CR1R2CR3R4H
            • tertiary carbocation more stable than primary so major product
        • Acylation
          • Benzene reacts with acyl chlorides in the presence of anhydrous AlCl3 under reflux at 50oC
            • R-COCl + AlCl3 --> R-CO+ + AlCl4-
          • C6H6 + R-COCl --> C6H5COR + HCl
            • The AlCl3 is a catalyst
        • Above 55oC  further substitution occurs
    • Phenylamine
      • Properties
        • is a much weaker base than aliphatic amines since the lone pair on the nitrogen atom is absorbed into the delocalised system and is thus not available for bonding with a proton
      • Preparation
        • main use of nitrobenzene is to make phenylamine
          • Nitrobenzene can be reduced to phenylamine 
            • Ni catalyst/H2 gas
            • and one of the following:         Hcl/Fe             Sn/Zn           SnCl2
            • C6H5NO2 + 6[H] --> C6H5NH2 + 2H2O
            • Hydrogenation/Reduction
    • Uses of Aromatic Compounds
      • Explosives
        • trinitrotoluene (TNT) is formed by the nitration of methylbenzene
      • Dyestuffs
        • Phenylamine can be converted into another important compound, benzenediazonium chloride by reaction with nitrous acid
          • Phenylamine + HNO2 +HCl -->  benzenediazonium chloride +2H2O
        • Benzenediazonium chloride can be used to make a number of different dyes
      • Polystyrene
        • Ethylbenzene is manufactured industrially from benzene and ethene in the presence of AlCl3 and HCl
          • Ethylbenzene can be dehydrogenated to form phenylethene, or “styrene” in the presence of iron oxide at high temperature
            • phenylethene can then be polymerized to form polystyrene (or polyphenylethene)


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