In Chapter 10 we looked at the π molecular orbitals for ethene and 1,3-butadiene (review
?)
Now we will look at the π molecular orbitals for benzene. With 6 C atoms contributing
to the π system, we need to create 6 molecular orbitals.
These are shown below. The most stable orbital, π1, is the all in-phase combination. We then have two
orbitals, π2 and π3,
that are still bonding but each with one node. There are then two orbitals
π4 and π5,
that are anti-bonding each with two nodes. Finally, the least stable orbital,
π6, is the all out-of-phase combination with
three nodes.
Once we put the π electrons into these molecular orbitals, we see that
maximum stability is being gained because all of the 6 π electrons completely fill the three bonding orbitals.
This is referred to as a closed shell π-electron
configuration.
