1. Aromatic Nitration - Mechanism
The combination of nitric acid and sulfuric acid produces NO2+ (nitronium ion), a powerful electrophile.
The reaction with benzene produces nitrobenzene. E+
Two Steps
Nu:
cationic intermediate – draw resonance structures

2. Aromatic Sulfonation What is the electrophile?
Add a sulfonic acid group (-SO3H) to the ring using sulfuric acid and SO3.
With –CF3, the new group is added meta.
What is the electrophile?

3. Aromatic Sulfonation
Reaction with a mixture of sulfuric acid and SO3 gas (“fuming sulfuric acid”).
Electrophile is sulfur trioxide (SO3) or its conjugate acid.
Reaction occurs via cationic intermediate and is reversible.

4. Review: EAS Reaction Conditions
Halogenation (Cl2 or Br2):
Benzene Nitration:
Aromatic Sulfonation:

5. Effect of Substituents
But what if the benzene ring has a substituent?
Q1 Where does the new group go?
Q2 Is the reaction faster or slower than benzene? x

6. Substituent Effects in Aromatic Rings
Substituents can make a ring more reactive or less reactive: “activators” vs. “deactivators”
Substituents also control orientation of the reaction: “ortho/para directors” vs. “meta directors”
least reactive
most reactive

7. Substituent Effects
Q. How do different substituents influence the rate of electrophilic aromatic substitution reactions? activate the ring = faster reaction deactivate ring = slower reaction
Q. How do different substituents effect orientation of the substitution reaction? (ortho/para vs. meta substitution)
Answer: Inductive Effects Resonance Effects

8. Inductive vs. Resonance Effects
Inductive Effect Resonance Effect
Based on: electronegativity conjugation
Electrons Move: via sigma bonds pi bonds/lone pairs
Distance: short-range may be long range
Overall Effect: electron cloud pi bonds and is shifted lone pairs move by electronegativity by resonance
Example: