AQA A Level Chemistry

Revision Notes

7.4.1 Structure of Benzene

Structure of Benzene

  • Aromatic molecules consist of one or more rings with conjugated π systems
  • Conjugated π systems arise from alternating double and single bonds in which the electrons are delocalised
  • Aromatic compounds are called ‘aromatic’ as they often have pleasant odours

 

Examples of aromatic compounds including benzene table

Organic Chemistry - Nomenclature of Functional Groups Aromatic Compounds, downloadable AS & A Level Chemistry revision notes

Shape of benzene & aromatic compounds

  • Benzene and other aromatic compounds contain sp2 hybridised carbons as two of their p orbitals have mixed with an s orbital
  • This means that each carbon atom in benzene and other aromatic compounds has one p orbital

 

Organic Chemistry - Sp2 Hybridisation in Aromatic Compounds, downloadable AS & A Level Chemistry revision notes

The carbon atoms in aromatic compounds are sp2 hybridized as two of their p orbitals mix with an s orbital

  • Each carbon atom in the ring forms three σ bonds using the sp2 orbitals
  • The remaining p orbital overlaps laterally with p orbitals of neighbouring carbon atoms to form a π bond
  • This extensive sideways overlap of p orbitals results in the electrons being delocalised and able to freely spread over the entire ring
  • Benzene and other aromatic compounds are regular and planar compounds with bond angles of 120o
  • The delocalisation of electrons means that all of the carbon-carbon bonds in these compounds are identical and have both single and double bond character
  • The bonds all being the same length is evidence for the delocalised ring structure of benzene

Organic Chemistry - Shape and Structure of Benzene, downloadable AS & A Level Chemistry revision notes

Like other aromatic compounds, benzene has a planar structure due to the sp2 hybridisation of carbon atoms and the conjugated π system in the ring

Electrophilic Substitution

Electrophilic Substitution

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