Michael McBride continues Yale's Freshman Organic Chemistry II with a lecture on radical-chain reactions. He opens with the reactivity-selectivity principle, explaining why bromine atoms discriminate more than chlorine atoms when abstracting hydrogen from carbon. He then works through the free-radical mechanism for HBr addition to alkenes, showing how it produces anti-Markovnikov regiochemistry rather than the ionic pathway's usual product. The middle of the lecture turns to kinetics, deriving rate laws for catalytic halogenation cycles and showing how chain termination steps can make the overall rate half-order in initiator concentration. The final segment examines how protonation and ionic charge on radicals and their reaction partners can override the expected regiospecificity. Recorded in Spring 2011 as part of Yale's CHEM 125B, the lecture runs through four chapters moving from qualitative principle to quantitative rate-law derivation, aimed at students already grounded in basic organic mechanisms.