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Part of OC-03 — Aromatic Hydrocarbons

EAS Reactions Comparison — Comparison Note

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Side-by-Side Comparison of Five EAS Reactions:

Feature	Halogenation	Nitration	Sulfonation	FC Alkylation	FC Acylation
Reagent	$Cl_{2}$ / $Br_{2}$	Conc. $HNO_{3}$	Fuming $H_{2}SO_{4}$	RCl	RCOCl
Catalyst	$FeCl_{3}$ / $FeBr_{3}$ / $AlCl_{3}$	Conc. $H_{2}SO_{4}$	None	$AlCl_{3}$	$AlCl_{3}$
Electrophile	$X^{+}$	$NO_{2}^{+}$ (nitronium)	$SO_{3}$	$R^{+}$ (carbocation)	R $CO^{+}$ (acylium)
Product	Aryl halide	Nitroarene	Arylsulfonic acid	Alkylbenzene	Aryl ketone
Reversible?	No	No	YES	No	No
Rearrangement?	N/A	N/A	N/A	YES	No
Polysubstitution?	Possible	Controlled by conditions	Controlled	YES	No (ring deactivated)

Critical Differences — FC Acylation vs. Alkylation:

Parameter	FC Alkylation	FC Acylation
Intermediate	$R^{+}$ (simple carbocation)	R $CO^{+}$ (acylium — resonance stabilized: R- $C^{+}$ =O ↔ R-C≡ $O^{+}$ )
Rearrangement	YES — 1° → 2° → 3° carbocation shift	NO — acylium resonance prevents rearrangement
Polysubstitution	YES — alkyl product activates ring further	NO — acyl product (-COR) deactivates ring
Preferred for synthesis?	Only for simple, unbranched products	YES — clean, single substitution

SMILES for acylium ion resonance: Form 1: [CH3][C+]=O ↔ Form 2: [CH3]C#[O+]

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