Chapter 12 : Reactions of Arenes. Electrophilic Aromatic
The following table shows the effect substituents have on both the rate and orientation of electrophilic aromatic
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 ?
||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
- 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,
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
- EWG remove electron density from the π system making it less
||© Dr. Ian Hunt, Department of Chemistry, University