Molecular Orbitals of Benzene
Shown below are the calculated molecular orbitals for the benzene (C6H6) molecule. These orbitals were calculated using the ab initio Hartree-Fock approach with a STO-3G basis set (which is a minimal basis set). In the simplest approximation, the six molecular orbitals shown below can be derived from the six 2pz atomic orbitals (one on each carbon atom).
| π* |  |
(empty) | |
| π* |  |
 |
(empty) |
| π |  |
 |
2 e- in each M.O. |
| π |  |
2 e- in M.O. | |
The lowest energy absorption for this molecule occurs in the ultraviolet region (benzene is colorless) and corresponds to transition of an electron from an occupied π orbital to an unoccupied π* orbital. (π → π*)