Overall reaction
C₆H₆ + (CH₃)₃CCl → (AlCl₃) C₆H₅C(CH₃)₃ + HCl
AlCl₃ turns an alkyl halide into a carbocation that alkylates the ring.
Name reaction · mechanism
Friedel–Crafts Alkylation
Friedel–Crafts alkylation attaches an alkyl group to an aromatic ring using an alkyl halide and a Lewis acid such as AlCl₃. The Lewis acid generates a carbocation (or a polarised complex), the ring attacks it to form an arenium ion, and loss of a proton restores aromaticity.
Mechanism step by step
- Carbocation. AlCl₃ pulls chloride off carbon
- Attack. The ring attacks the carbocation
- Deprotonation. Cl⁻ (from AlCl₄⁻) takes H⁺; AlCl₃ is regenerated
Each step is checked electron by electron: the curly arrows give exactly the structures drawn.
Key points
- Primary halides rearrange: 1-chloropropane also gives cumene.
- The alkylated ring is more reactive than benzene, so polyalkylation is common.
- Strongly deactivated rings (nitrobenzene) and anilines do not react.
- Acylation then reduction avoids both problems.
For JEE and NEET
- Carbocations rearrange: n-propyl chloride gives mainly isopropylbenzene.
- Polyalkylation: the alkylated product is more reactive than benzene.
- Fails on strongly deactivated rings (nitrobenzene) and on aniline (NH₂ binds AlCl₃).
- Aryl and vinyl halides cannot be used.
FAQ
Why does Friedel–Crafts alkylation give rearranged products?
Primary carbocations (or their complexes) undergo hydride/alkyl shifts to more stable secondary or tertiary cations before attack.
How can polyalkylation be avoided?
Use a large excess of the arene, or do Friedel–Crafts acylation and then reduce the ketone (Clemmensen or Wolff–Kishner).
Why does aniline not react?
The basic NH₂ group complexes with AlCl₃, putting a positive charge next to the ring and deactivating it.
Draw it in MolDraw
The button above opens the complete figure — overall reaction, numbered mechanism and key points — as ordinary editable structures. Change substituents, recolour atoms, or export a PNG, SVG or chemfig code for notes and slides. The same figure is in the Templates panel under Name reactions.