This lecture covers rearrangement reactions, including sigmatropic rearrangements like Cope, Claisen, and Wagner-Meerwein rearrangements, as well as cationic rearrangements such as 1,2-hydride shifts and 1,2-alkyl shifts. It also discusses rearrangements involving formal electron-sextet, like Baeyer-Villiger oxidation and Beckmann rearrangement. The lecture delves into specific examples like the Hofmann rearrangement and Curtius reaction, highlighting the significance of structural modifications resulting from these reactions.