Michael McBride continues Yale's Freshman Organic Chemistry II with a lecture on aromatic substitution chemistry. He opens with the discovery of Friedel-Crafts alkylation and acylation, then covers how chemists avoid unwanted carbocation rearrangements in these reactions. The lecture moves into synthetic strategy, showing how diazonium salts let chemists reach a wide range of substituted benzenes that direct substitution alone cannot produce. McBride explains nucleophilic aromatic substitution on electron-poor rings and connects it to NADH reduction in biochemistry. He closes with benzylic reactivity and steric hindrance, tracing their role in early twentieth century organic chemistry through Moses Gomberg's work on triphenylmethyl radicals. Recorded in spring 2011 as part of the Open Yale Courses series, the lecture is organized into five chapters and builds directly on prior classes covering aromatic substitution fundamentals, aimed at students already grounded in reaction mechanisms.