Yale's Freshman Organic Chemistry II (CHEM 125B), taught by Michael McBride, opens with Moses Gomberg's studies of hexaphenylethane and his claim to have made the first trivalent carbon compound, the triphenylmethyl radical, framed as the moment fundamental organic chemistry took root in America. McBride then turns to whether protonated cyclopropane intermediates explain rearrangements in Friedel-Crafts alkylation, using isotopic labeling evidence to test the idea. The lecture moves into carbonyl chemistry, showing how C-13 NMR chemical shifts of aldehydes and ketones were established empirically, and distinguishing the carbonyl group's thermodynamic stability from its kinetic reactivity. He covers acid- and base-catalyzed reactions that proceed through enol or enolate intermediates, the four reaction patterns of carboxylic acids, and the multistep mechanism of acid-catalyzed acetal hydrolysis. Recorded in 2011 as part of the Open Yale Courses series.