A-Level Terminology and mechanisms of organic reactions: worked solution

Question

Lay out the mechanism by which benzene is converted to acetophenone, drawing the electron-pair shifts as curly arrows together with the charges and any lone pairs that matter.

Acetophenone (C6H5COCH3) is made by Friedel-Crafts acylation of benzene. The electrophile is the acylium ion CH3CO+ (generated from CH3COCl + AlCl3). Step 1: a curly arrow goes from the benzene ring pi system to the positively charged carbon of CH3CO+, forming a new C-C bond and a positively charged, non-aromatic intermediate (arenium/Wheland ion) in which the ring carbon bears the acyl group and an H, and the ring carries a delocalised + charge. Step 2: a curly arrow from the C-H bond of that carbon back into the ring regenerates the aromatic ring and releases H+ (taken up by AlCl4-), giving acetophenone.