Resonance Structures: Benzene Rings

What we learned:

• Resonance structures that involve benzene rings require us to identify what type of interaction the substituent has with the benzene ring
  • A substituent is a group directly attached to the benzene ring
  • Substituents can be electron donating to the ring, or electron withdrawing from the ring
• To identify what type of interaction the substituent has with the benzene ring, we need to look at the atom bonded directly to the ring itself, and the atom bonded to that atom
  • We call these the X and Y atoms
• If the electronegativity of the X atom is greater than the electronegativity of the Y atom: that group has an electron donating interaction with the benzene ring
  • This will cause a lone pair to form a pi bond between the benzene ring and the X atom, creating a formal negative charge on the benzene ring in the resonance structures
  • The pi system will have a partial negative charge at every place the formal negative charge was in the resonance structures
• If the electronegativity of the Y atom is greater than the electronegativity of the X atom: that group has an electron withdrawing interaction with the benzene ring
  • This will cause a pi bond from the benzene ring to be drawn out to form a double bond between the benzene ring and the X atom, creating a formal positive charge on the benzene ring
  • The pi system will have a partial positive charge at every place the formal positive charge was in the resonance structures