The diagram below is a Frost-Hückel
circle mnemonic. A polygon representing the ring system, in
this case a regular hexagon for benzene, is inscribed in a
circle with a vertex at the bottom. The energy levels of the
six-π-MO's are placed at each vertex. The energy of an
isolated p-orbital is taken as passing through the center of
the circle. From the geometry of a regular hexagon, there
should be equal separation of the three energy levels.
Compare with the energies on the right. There are three
bonding MO's and three anti-bonding MO's. MO's
Ψ2
and Ψ3 are degenerate (same energy) bonding orbitals while Ψ4* and Ψ5*
The bonding MO's are coded in green; anti-bonding MO's in red.
|
Ψ6-
Antibonding
Surfaces
6 nodes
|
Ψ4-
Antibonding
Surfaces
4 nodes
|
Ψ5-
Antibonding
Surfaces
4 nodes
|
Ψ2-Bonding
Surfaces
2 nodes
|
Ψ3-Bonding
Surfaces
2 nodes
|
Ψ1-Bonding
Surfaces
0 nodes
|
|