Problems and exercisesAromatic Electrophilic Substitution

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1. Which is the electrophile?

In the following electrophilic aromatic substitution (SEAr) reactions, indicate which is formally the electrophilic species.

Five reactions of benzene: with Cl₂/FeCl₃, Br₂/FeBr₃, SO₃/H₂SO₄, 1-chloropropane/AlCl₃ (gives isopropylbenzene) and propanoyl chloride/AlCl₃ (gives propiophenone)

2. Why a catalyst?

What role do FeBr₃ in the bromination and H₂SO₄ in the nitration of benzene play?

3. Benzenonium

Draw the resonance forms of the benzenonium ion formed in the chlorination of benzene. At which positions relative to the attacked carbon does the positive charge lie?

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