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Chapter 12 :  Reactions of Arenes. Electrophilic Aromatic Substitution
Ch 12 contents

Substituent Effects(contd.)

The following table shows the effect substituents have on both the rate and orientation of electrophilic aromatic substitution reactions.

Study Tip:

This is a VERY important table ! It is worth knowing.... your best understanding will come if you learn HOW it works.
It's application goes way beyond electrophilic aromatic substitution reactions.

Key concepts to review ?  Resonance and electronegativity

Table of Substituent Effects These effects are a combination of RESONANCE and INDUCTIVE effects (see next page)
The effects are also important in other reactions and properties (e.g. acidity of the substituted benzoic acids).

Here are some general pointers for recognising the substituent effects:

  • The H atom is the standard and is regarded as having no effect.
  • Activating groups increase the rate
  • Deactivating groups decrease the rate
  • EDG = electron donating group
  • EDG can be recognised by lone pairs on the atom adjacent to the π system, eg: -OCH3
  • except -R, -Ar or -vinyl (hyperconjugation, π electrons)
  • EWG = electron withdrawing group
  • EWG can be recognised either by the atom adjacent to the π system having several bonds to more electronegative atoms, or
  • having a formal +ve or δ +ve charge, eg: -CO2R, -NO2
  • EDG / activating groups direct ortho / para
  • EWG / deactivating groups direct meta
  • except halogens (-X) which are deactivating BUT direct ortho / para
  • EDG add electron density to the π system making it more nucleophilic
  • EWG remove electron density from the π system making it less nucleophilic.

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organic chemistry © Dr. Ian Hunt, Department of Chemistry University of Calgary