Guest lecturer G. Barney Ellison, speaking in Yale's Freshman Organic Chemistry II course taught by Michael McBride, explains how chemists determine bond dissociation energies for polyatomic molecules. He starts with the relatively simple spectroscopic measurements available for diatomic molecules, then shows how flowing-afterglow mass spectrometry and negative-ion photoelectron spectroscopy combine with free-radical kinetics and heats-of-formation data to pin down the O-H, C-H, and C-O bond strengths in methanol and related compounds. The lecture walks through acidity measurements in the flowing afterglow, radical equilibrium methods for C-H bonds, and the potential errors in deriving C-O bond energies from heats of formation. A closing discussion tackles how these precise numbers reshape the understanding of chemical bonding and resonance stabilization, with student questions on hot bands and resonance closing out the session.