Michael McBride continues Yale's Freshman Organic Chemistry II with a lecture on carbon-13 and two-dimensional NMR before turning to electrophilic aromatic substitution. He explains how proton decoupling simplifies C-13 spectra, then shows how dilute double labeling with C-13 confirmed the rearrangement scheme in lanosterol biosynthesis. Two-dimensional NMR comes next, covering the correlations used to determine protein structure and to identify the mechanism behind a fast carbocation rearrangement. The lecture then shifts to electrophilic aromatic substitution, describing the two-step association-dissociation mechanism through a cyclohexadienyl cation intermediate, and how substituents on a benzene ring change the stability of that intermediate and the resulting product ratios. McBride closes with the history of electrophile activation, crediting Friedel and Crafts for their foundational work in Paris. Recorded in Spring 2011 as part of Yale's Open Courses, the talk moves briskly through dense spectroscopic and mechanistic material with chalkboard diagrams and reaction schemes.