Organic Chemistry: arenes -5

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  • Created by: Shannon
  • Created on: 16-04-15 09:24
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  • Arenes
    • Reactions of benzene
      • Nitration
        • Concentrated nitric and sulphuric acid
          • HNO3 + H2SO4 -> HSO4- + NO2+ + H2O
          • Harsh conditions needed in order to form electrophile
      • Bromination
        • Br2 + FeBr3
      • Chlorination
        • Cl2 + FeCl3
      • Freidel crafts acylation
        • AlCl3 + O=R-Cl
      • Freidel crafts akylation
        • AlCl3 + R-Cl
      • Sulfonation
        • Under reflux with "Fuming sulfuric acid"
        • H2SO4 + SO3 -> HSO4- + HSO3+
      • The ring of delocalised electrons makes addition reactions thermodynamically unfavourable
        • Undergoes electrophilic substitution reactions
          • This restores aromaticity
      • The Wheland intermediate
        • Positive charge is not located in one place
          • Resonance structures
      • Combustion
        • Burns with an extremely smoky flame
      • Hydrogenation
        • Cycloalkane formed
        • Delocalised ring destroyed
    • Structure and stability of benzene
      • Reactivity
        • Theoretical
          • Reacts with bromine water
        • Actual
          • No reaction observed
          • Benzene more stable than other alkenes
      • Enthalpy of formation
        • Theoretical
          • Value of +243 kJmol-1
        • Actual
          • Value of +49kJmol-1
          • More stable than Kekule structure would allow us to believe
      • IR spectra
        • Theoretical
          • Non-symmetrical
        • Actual
          • Spectra more symmetrical than predicted
      • Bond lengths
        • Theoretical
          • Mixture of double bonds and single bonds - 0.134nm & 0.154nm
        • Actual
          • Bonds lengths are all identical at 0.139nm
      • Thermodynamics
        • Theoretical
          • 3x that of cyclohexene, around -340 - -360 kJmol-1
        • Actual
          • It is -208 kJmol-1
          • More stable than predicted
      • Thermodynamics
        • Theoretical
          • Varying electron density dependent on bond type - e.g more dense around C=C
        • Actual
          • Even distribution throughout molecule
      • Actual structure
        • Formation of a ring of delocalised electrons
          • Electron density aboive and below the plane of the carbon atoms
            • This contributes to the stability of the molecule
    • Phenol v Benzene
      • In phenol, the oxygen atom of the -OH has a lone pair of electrons
        • This can contribute to the electron density of delocalised ring
          • = MESOMERIC EFFECT
          • This makes the ring more attractive to electrophiles, making reactions easier to occur

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