Electrophilic Aromatic Substitution

Electrophilic aromatic substitution is a reaction in which an electrophile replaces a hydrogen atom in an aromatic compound. The most common electrophiles used are nitronium ion (NO2+), halogens (X2), and sulfur trioxide (SO3). The reactivity of the aromatic ring towards electrophilic substitution depends on the presence of electron-releasing or electron-withdrawing groups on the ring.

Phenol is the most reactive towards electrophilic substitution because of the presence of a hydroxyl group (-OH) which is an electron-donating group. The hydroxyl group donates electron density to the benzene ring, making it more nucleophilic and hence more reactive towards an electrophile. The hydroxyl group also stabilizes the intermediate formed during the reaction by forming a resonance structure.

On the other hand, chlorobenzene and toluene are less reactive because of the presence of electron-withdrawing groups (-Cl and -CH3 respectively) which withdraw electron density from the benzene ring, making it less nucleophilic and hence less reactive towards an electrophile.

Conclusion

In conclusion, phenol is the most readily attacked by an electrophile because of the presence of a hydroxyl group which is an electron-donating group, increasing the reactivity of the benzene ring towards an electrophile. Chlorobenzene and toluene are less reactive because of the presence of electron-withdrawing groups which decrease the reactivity of the benzene ring towards an electrophile.