Consider conjugated molecules (Alternation of single and double bonds)
Pi orbitals are treated separately from the sigma orbitals.
Consider sigma bonds to be fixed and concentrate on finding the energies of the pi bonds and antibonds.
The Pi molecular orbital energy level diagrams of conjugated molecules can be constructed using a set of approximations suggested by Erich Hückel.
All overlap integrals (S) are set equal to zero.
All resonance integrals () between non-neighbors are set equal to zero.
All remaining resonance integrals are set equal.
Restricted to planar conjugated hydrocarbons