Concept:In Friedel-Crafts acylation, the Lewis acid catalyst serves specifically to strip a chloride ion from the acyl chloride, producing the active electrophile.
Formula:$$ \text{CH}_3\text{COCl} + \text{AlCl}_3 \rightarrow \text{CH}_3\text{C}^+=\text{O} + \text{AlCl}_4^- $$
Solution:- Acetyl chloride (\( \text{CH}_3\text{COCl} \)) loses \( \text{Cl}^- \) to \( \text{AlCl}_3 \).
- This generates the highly reactive, resonance-stabilized acylium ion: \( \text{CH}_3\text{C}^+\text{O} \).
- This acylium ion acts as the direct electrophile that attacks the benzene ring to yield acetophenone.
Why other options are incorrect:- \( \text{C}^+\text{H}_3 \) is a methyl carbocation, which would be the electrophile for Friedel-Crafts alkylation using methyl chloride, not acylation.
- \( \text{AlCl}_3 \) is the catalyst, not the attacking electrophile on the ring.
- \( \text{CH}_3\text{COCl} \) is the neutral starting reagent, not yet activated into an electrophile.
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