Friedel-Crafts alkylation and Friedel-Crafts acylation reactions are electrophilic aromatic substitution reactions that form C-C bonds. When you treat benzene with an alkyl chloride, nothing happens. If you dope in a Lewis acid like AlCl3 (aluminum trichloride), you get a reaction—the substitution of a H on the benzene ring for the alkyl group. This reaction is called Friedel-Crafts alkylation, see below:
Trick Alert: How do most organic chemistry professors trick you on the Friedel-Crafts alkylation?
It turns out that the combination of AlCl3 and an alkyl chloride forms a carbocation that is liable to rearrangements (e.g. hydride shifts). If you think about the alkyl chloride as a carbocation source (cover up the Cl with your thumb and put a + on the carbon the Cl is attached to). Professors love to trick you on this. So watch out. If you have an alkyl chloride that will give a rearrangeable carbocation, then it may rearrange.
How do you overcome the rearrangement problem?
Answer: Friedel-Crafts Acylation
The Friedel-Crafts acylation reaction overcomes the rearrangement problem faced by the complementary Friedel-Crafts alkylation reaction. However, your final product is a ketone that often must be reduced to the alkane. To do this, you can do either a Clemmensen reduction (acidic) or a Wolff-Kishner reduction (basic).
