3.01 | The MO-Diagram of π-Conjugated Systems I

Monday June 17th 2024 | In this online lesson, we take our knowledge on how to construct the MO-diagram of complex main group elements to organic compounds that have π-Conjugated Systems. We start with the most simple example, ethylene, which is also the first example in which there is no central atom. We construct the MO-Diagram by grouping the carbon atoms and hydrogen atoms separately and determining their symmetry adapted linear combinations. By doing so we realize that for the two carbon atoms, the MO-diagram of C2 fragment is generated including the bonding and anti-bonding interaction. Having established the symmetry adapted linear combinations, we constructed the MO-diagram of ethylene and arranged the molecular orbitals (energy wise) according to the number of nodes we observe. Now that the MO-diagram of ethylene is established, we move forward to the MO-diagram of butadiene. When we establish the irreducible representations of the four carbon atoms, we find that the Pz orbitals -that form the π-conjugated system – are always different, which turns out to be a general rule.

The link to the video can be found below: