Aromatics

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Aromatics

• AH Chemistry, Unit 3(b)

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Bonding in benzene
What information about bonding do these structure
suggest to you?
sp2 hybridisation
Sigma and pi bonding
Electron delocalisation
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Reactivity of benzene
How reactive would you say benzene is?
Not very.
Why?
The delocalisation of 6 ? electrons over the ring
stabalise the structure.
What does it react with?
(Strong) electrophiles
What is its characteristic reaction type?
Electrophilic substitution, producing substituted
benzene rings.
What are the products used for?
Medicines, dyes, insecticides, pesticides and
resins.
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Stability of benzene
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Characteristic reactions

• Halogenation (chloronation and bromination) to
  produce chlorobenzene and bromobenzene
• Alkylation to produce alkylbenzenes
• Nitration to produce nitrobenzene
• Sulphonation to produce benzene sulphonic acid

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General mechanism 1
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General mechanism 2
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General mechanism 3
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Bromination
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Chlorination
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Alkylation (Friedel-Crafts alkylation)
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Nitration
(concentrated)
(concentrated)
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Sulphonation
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Acidity of phenol

• Phenol is a weak acid
• Phenoxide ion is stabalised due to the negative
  charge of the oxygen atom is delocalised over the
  ring.
• Phenol is therefore more acidic than aliphatic
  alcohols.

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Basic nature of aminobenzene (analine)

• Phenylamine is basic
• There is delocalisation of the lone pair of
  electrons on the nitrogen atom in aminobenzene,
  into the aromatic system
• It therefore accepts a proton less readily than
  ammonia of aliphatic amines and is less basic