The Shape of Aromatic Molecules (CIE A Level Chemistry)

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Shape of Benzene & Aromatic Molecules

  • 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 table

Functional group Example Name
Arene  
propylbenzene-highlighting-functional-group 
Propyl benzene
Chlorobenzene  2-methylchlorobenzene-highlighting-functional-group
 
2-methylchlorobenzene
Phenol  23-dimethyl-phenol-highlighting-functional-group
 
2,3-dimethyl phenol

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

 sp2 hybridisation

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

The carbon atoms in aromatic compounds are sp2 hybridised 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

The planar 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

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Richard

Author: Richard

Expertise: Chemistry

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.