Molecular Orbitals: Properties of Conjugated Systems

This lecture covers the concept of molecular orbitals in π-conjugated systems, focusing on the properties of molecules with multiple bonds. It begins with an overview of bond lengths and energy barriers for rotation in various conjugated systems, such as 1,3-butadiene and benzene. The instructor explains the differences between conjugated, cumulated, and isolated double bonds, emphasizing how conjugated systems exhibit unique electronic interactions. The discussion progresses to cyclic conjugated systems and the stability of aromatic compounds, highlighting Hückel's rule. The lecture also introduces the electron in a 1D box model as a simplified representation of linear conjugated systems, illustrating how molecular orbitals can be delocalized across multiple atoms. The energy levels of frontier orbitals in butadiene and hexatriene are analyzed, demonstrating how bond orders can be calculated. Finally, the instructor addresses the electronic structure of polyacetylene and the implications of Hückel theory for understanding the properties of conjugated systems, including their conductivity and reactivity.