3.02 | The MO-Diagram of π-Conjugated Systems II

Monday June 24th, 2024 | Today we continue with the analysis of the MO-Diagrams of π-conjugated systems. In particular we continue our investigation into the MO-diagram of butadiene. Last week we already prepared the SALCs of the hydrogen atoms. Today we continue with our analysis and determine the SALCS of the Px, Py, and Pz orbitals of the carbon atoms. As previously established the symmetry of the Pz orbitals are distinct from the Px and Py orbitals resulting in a unique set of SALCs that are are part of the frontier orbitals (HOMO & LUMO) of butadiene. By using the character table and taking into account the number of (symmetric) nodes that are expected, we are able to construct arrange the four molecular orbitals of butadiene that form the π-conjugated system. Next we applied the same methodology to construct the partial MO-diagram of benzene, by arranging the found molecular orbitals according to their symmetry and to the number of nodes they present. Analysis of these orbitals enables to understand their reactivity towards electrophiles and nucleophiles. Finally at the end of the lecture, we started to make progress in constructing the SALCs of the hydrogen atoms in cyclopropane.

The video to the lecture can be found below: