Answer
🧪 Reactivity Toward Br₂ and FeBr₃
🔍 Question:
Which compound will undergo reaction with Br₂ and catalytic FeBr₃ the fastest?
⚡ Key Concept: Electrophilic Aromatic Substitution (EAS)
In bromination of aromatic rings, the reaction is accelerated by electron-donating groups (EDGs) and slowed down by electron-withdrawing groups (EWGs).
- EDGs activate the ring → increase reactivity
- EWGs deactivate the ring → decrease reactivity
📊 Reactivity Chart
| Group | Type | Effect on EAS | Examples |
|---|---|---|---|
| –OH, –OCH₃, –NH₂ | EDG | Strong Activation | Anisole, phenol |
| –CH₃ | EDG | Moderate Activation | Toluene |
| None | Neutral | Reference | Benzene |
| –NO₂, –COOH, –CN | EWG | Deactivation | Nitrobenzene, benzoic acid |
✅ Fastest Reacting Compound
The compound with the strongest activating group will react the fastest.
→ Anisole (methoxybenzene, Ph–OCH₃) reacts the fastest with Br₂/FeBr₃.
This is due to the strong electron-donating effect of the methoxy group through resonance and induction, which enhances the reactivity of the aromatic ring toward electrophilic attack.
🧠 Summary
- EDGs increase reactivity toward bromination.
- EWGs decrease reactivity.
- Anisole is the most reactive toward EAS with Br₂ and FeBr₃.