Rates of Reaction

1. Rates of Reaction Rates of electrophilic aromatic substitutions reactions increase with electron donating groups (EDG) on the ring. Rates decrease when electron density is removed from the ring: E+ Where will the electrophile go? These rings therefore will react faster. x

2. Electron Donation – Ring is More Reactive Electron donation by resonance: Flow of pi electrons donated to ring is shown by resonance structures. Electron donation by induction:

3. Electron Donation – Ring is More Reactive In an electrophilic reaction, where will the electrophile find the most electron density? Aminobenzene is more reactive that benzene.(Rate of electrophilic reaction is higher.) The -NH2 substituent is an activatinggroup.

4. Electron Withdrawl – Ring is Less Reactive Electron withdrawl by resonance: Flow of pi electrons removed from ring is shown by resonance structures. Electron withdrawl by induction: Based on electronegativity

5. Electron Withdrawl – Ring is Less Reactive In this electrophilic reaction, where is the most electron density? Trifluoromethylbenzene is less reactive that benzene. The -CF3 substituent is a deactivatinggroup.

6. Substituent Effects in Aromatic Rings least reactive most reactive The more electron density a substituent donates, the faster the rate of AES reaction. Slowest reactions are seen with groups that withdraw the most electron density.

7. Summary – Substituent Effects Activating groups donate electrons to the ring, stabilizing the carbocation intermediate Deactivating groups withdraw electrons from the ring, destabilizing intermediate slower faster x

8. Substituent Effects Q. How do different substituents influence the rate of electrophilic aromatic substitution reactions? (activate or deactivate the ring) Q. How do different substituents effect the orientation of the substitution reaction? (ortho/para vs. meta substitution) Answer: Inductive EffectsResonance Effects x