CIE A Level Chemistry (9701) 2019-2021

Revision Notes

7.3.3 Directing Effects of Substituents on Arenes

Arenes: Directing Effects of Substituents

  • Arenes readily undergo electrophilic substitution of one of their hydrogen atoms with another species
  • Substituents that are already present on the arenes can affect where the substitution of the hydrogen atom on the arene takes place
    • These groups are said to direct substitution reactions to different ring positions

Electron-withdrawing & -donating groups

  • The substituents on the arenes can either be electron-withdrawing or electron-donating groups
  • Electron-withdrawing substituents remove electron density from the π system in the benzene ring making it less reactive
    • These groups deactivate attack by electrophiles and direct the incoming electrophile to attack the 3 and/or 5 positions
    • For example, the nitro group in nitrobenzene is an electron-withdrawing group
      • Upon bromination of nitrobenzene, the bromine electrophile will be directed to the 3 and/or 5 position
      • The products are 3-chloronitrobenzene and 5-chloronitrobenzene
    • Electron-donating substituents donate electron density into the π system of the benzene ring making it more reactive
      • These groups activate attack by electrophiles and direct the incoming electrophile to attack the 2, 4 and/or 6 positions
      • For example, the methyl group in methylbenzene is an electron-donating group
        • Upon bromination of methylbenzene, the bromine electrophile will be directed to the 2 and/or 4 position
        • The products are 2-chloromethylbenzene and 4-chloromethylbenzene

Electron-withdrawing & -donating substituents table

Hydrocarbons - Electron withdrawing and donating substituents table, downloadable AS & A Level Chemistry revision notes

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Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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