Friedel-Crafts acylation involves the formation of a new C-C bond between a benzene ring and an acyl group. Specifically, when benzene reacts with an acyl chloride like acetyl chloride in the presence of a Lewis acid catalyst, it forms an acylbenzene product like acetophenone. The reaction mechanism proceeds in three steps: 1) the Lewis acid activates the acyl chloride to form an acylium ion, 2) the acylium ion attacks the aromatic ring, and 3) proton transfer regenerates the aromatic system.