3.4.6 Aromatic Chemistry - Delocalisation stability

Specification

Students should:
  • understand that delocalisation confers stability to the molecule
  • be able to use thermochemical evidence from enthalpies of hydrogenation to illustrate this principle

Delocalisation stabilisation

Delocalisation means spreading out of electrons over more than two nuclei. This has the effect of making the negative electron density less focussed and it stabilises the species, be it an ion or a molecule.

This stabilisation effect is apparent in many areas of chemistry, both inorganic and organic. Benzene is a very good example of how delocalisation leads to stabilisation of the molecule. This can be shown by comparison of the energy released by the hydrogenation of cyclohexene and benzene.

Delocalisation stabilisation in benzene


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