The structure of benzene

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The structure of benzene

• L.O.
• Explain the structure of benzene.
• Use evidence from enthalpies of
• hydrogenation to illustrate aromatic stability.

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Starter You are a great chemist called Kekulé
who has heard that Faraday has discovered a new
compound. The molecular formula is C6H6. Propose
a structure for this new compound
Clue he had a dream.
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STRUCTURE OF BENZENE
Benzene C6H6
Its structure was a mystery for many years -
until Kekules dream.
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STRUCTURE OF BENZENE
Problems with Kekules structure
1) C-C bonds are all the same length (between C-C
and CC length).
2) Benzene does not undergo addition reactions
readily (e.g. with bromine water).
3) Do not get isomers like this
4) ?H hydrogenation about 152 kJ mol-1 less than
expected.
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• Each carbon has three covalent bonds one to a
  hydrogen atom, and the other two carbon atoms.
  The fourth electron of each carbon is a
  p-orbital. There are six of these. The electrons
  in the p-orbitals overlap and are delocalised.
• The delocalised system makes benzene unusually
  stable (aromatic stability)

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STRUCTURE OF BENZENE
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STRUCTURE OF BENZENE
6 electrons in a delocalised ? bond
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STRUCTURE OF BENZENE
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STRUCTURE OF BENZENE
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HYDROGENATION OF BENZENE
-152 kJmol-1 delocalisation energy
Enthalpy (kJ mol-1)
-208
-120
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• You will create an A3 poster which will show the
  different representations of benzene. You should
  include diagrams of at least three different
  representations of benzene. You will explain how
  each model shows the structure and any drawbacks
  to the model. You should also include information
  about who discovered the structure of benzene and
  how this was done.

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• Task
• worksheet

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NAMING AROMATIC COMPOUNDS
methylbenzene (toluene)
chlorobenzene
nitrobenzene
benzenecarboxylic acid (benzoic acid)
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NAMING AROMATIC COMPOUNDS
1,3-dimethylbenzene (m-xylene)
4-methyl-1-chlorobenzene
2-hydroxybenzenecarboxylic acid
3,5-dinitrobenzenecarboxylic acid
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NAMING AROMATIC COMPOUNDS
phenylamine (aniline)
2-phenylbutane

phenylethene
phenylethanone
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NAMING AROMATIC COMPOUNDS
phenylethanoate
methyl benzenecarboxylate (methyl benzoate)
N-phenylethanamide
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NAMING AROMATIC COMPOUNDS
phenol
benzene-1,2-diol
2-nitrophenol
2,4,6-trichlorophenol (TCP)