This lecture covers the theory and practical aspects of finding transition states and barrier heights in chemical reactions. Starting with the synthesis of propylene oxide, the instructor explains the importance of transition state theory and the minimum energy path. The lecture delves into visualizing transition states in a potential energy surface and the intrinsic reaction coordinate. Practical exercises involve constructing a guess geometry, constrained optimization, and analyzing potential energy profiles. The session concludes with visualizing trajectories and analyzing bonds to understand the stereochemistry and transition state structures.