Electrophilic Aromatic Substitution Reactions

Resonance Effect
Inductive Effect
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Two major effects play a role:

• Resonance Effect
• Inductive Effect:

Resonance Effect:

• Through pi (double bond) system
• Strong effect
• Can be e- Donating (ortho-para directing) or Withdrawing (meta directing)

Resonance Donating Effect (ortho-para directing, activates - i.e. more reactive than benzene) - can often be recognized by lone pair of e- on atom directly attached to aromatic ring

Resonance Withdrawing Effect (meta directing, deactivates - i.e. less reactive than benzene) - it can often be recognized by double bond (often with Z=oxygen) conjugated to aromatic ring

Inductive Effect:

• Through sigma (single bond) system
• Weaker effect
• Can be e- Donating (ortho-para directing) or Withdrawing (meta directing)
  
  

Inductive Donating Effect:(ortho-para directing, activates - i.e. more reactive than benzene) - often caused by an alkyl group

Inductive Withdrawing Effect (meta directing, deactivates - i.e. less reactive than benzene) - often caused haloalkyl group

Multiple Substituents:

• Position of reaction is controlled by strongest donating group
• substitution between meta substituents rare (very difficult because of steric crowding)