Q.Outline the mechanism of the Friedel-Crafts alkylation of benzene with chloromethane and anhydrous $\text{AlCl}_3$, and state one practical limitation of this reaction.

Anhydrous aluminium chloride, a strong Lewis acid, coordinates to the lone pair on chloromethane's chlorine atom, weakening the $\text{C--Cl}$ bond and helping to generate a methyl-cation-like electrophile (or a strongly polarised complex behaving like one): $\text{CH}_3\text{Cl}+\text{AlCl}_3 \rightarrow \text{CH}_3^++\text{AlCl}_4^-$. This electrophile then attacks the benzene ring by the same mechanism as any other EAS reaction -- forming a resonance-stabilised arenium ion, then losing $\text{H}^+$ (removed by $\text{AlCl}_4^-$, which also regenerates the $\text{AlCl}_3$ catalyst) to rearomatise -- giving toluene, $\text{C}_6\text{H}_5\text{CH}_3$, as the product. Two practical limitations follow directly from the mechanism. First, because a genuine (or carbocation-like) intermediate forms, a LESS stable primary carbocation (from a less-simple alkyl halide than $\text{CH}_3\text{Cl}$) can undergo a hydride or alkyl shift to rearrange into a more stable carbocation before it ever attacks the ring, so the alkyl group actually installed can be a rearranged, more-branched one rather than the group originally present on the halide. Second, the alkylbenzene PRODUCT is more electron-rich, and therefore MORE reactive toward further electrophilic attack, than benzene itself (the alkyl group donates electron density into the ring) -- so, unless the alkyl halide is us …

Identify AlCl3's role as generating the carbocation electrophile, then apply the standard three-stage EAS mechanism; separately reason about WHY the product is more reactive than the start …

Forgetting the carbocation-rearrangement risk for anything beyond a simple, already-stable alkyl halide like methyl or tert-butyl chloride; assuming the reaction automatically stops after one substitution, when in fact controlling s …