So, what exactly is a lewis athens based reaction? So, a lewis athens based reaction is the interaction between a filled molecular orbital, as we saw here, and an antimolecular orbital. And this is known as a homolumo interaction. Homo simply meaning highest occupied molecular orbital, and lumo, meaning lowest unoccupied molecular orbital. So if we go back to the first step in this additional reaction, we see that our homo, the highest occupied molecular orbital, is the pi bond. So this is our lowest base.