EAS Sulfonation: Installing –SO₃H (Reversible Aromatic Substitution)

Master aromatic sulfonation: SO3/H2SO4 electrophile, sigma complex mechanism, and why sulfonation is reversible (useful as a blocking group).

Reaction: Arene → aryl sulfonic acid
What it does: Adds SO3H group to aromatic ring
Typical reagents: SO3/H2SO4 (fuming sulfuric acid)
Key intermediate: Sigma complex
Driving force: Re-aromatization by deprotonation
Exam type: Predict regio
Exam type: Mechanism steps

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