What makes a ring special: conjugation and delocalization, the four conditions for aromaticity, Hückel's 4n+2 rule, and how to read any ring as aromatic, antiaromatic, or nonaromatic.
The four conditions for aromaticity and Hückel's 4n+2 rule
Aromatic vs antiaromatic vs nonaromatic, with worked examples
Counting π electrons, including heteroatom lone pairs
Resonance energy, MO basics, and benzylic/allylic stabilization