Substituent Effects: Electrophilic Aromatic Substitution

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Substituent EffectsElectrophilic Aromatic
Substitution

• Substituents that are capable of donating
  electrons into the benzene ring will stabilize
  both the carbocation intermediate and the
  transition state leading to its formation
• Increases the rate of electrophilic aromatic
  substitution
• Substituents that withdraw electrons from the
  benzene ring will destabilize the carbocation
  intermediate and the transition state leading to
  its formation
• Decreases the rate of electrophilic aromatic
  substitution

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Ortho, Para, and Meta Directing Substituents

• All meta directing substituents have a positive
  or partial positive charge on atom adjacent to
  ring
• All ortho-para directing substituents have at
  least one lone-pair of electrons on atom adjacent
  to ring.

ortho-para
ortho-para
meta
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• TNT, a pale yellow solid, melts at 83C, and
  explodes at 240C. Supplying TNT with activation
  energy produces N2, CO, CO2, H2O, and lots of
  energy in a chemical chain reaction.

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Why is TNT so explosive?!

• TNT is explosive for two reasons. First, it
  contains the elements carbon, oxygen and
  nitrogen, which means that when the material
  burns it produces highly stable substances (CO,
  CO2 and N2) with strong bonds, so releasing a
  great deal of energy.
• The second fact that makes TNT explosive is that
  it is chemically unstable - the nitro groups are
  so closely packed that they experience a great
  deal of strain and hindrance to movement from
  their neighboring groups. Thus it doesn't take
  much of an initiating force to break some of the
  strained bonds, and the molecule then flies
  apart.

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Nucleophilic Aromatic Substitution Reactions
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p orbitals in a normal triple bond p
orbitals in benzyne