The Hückel
approximations
The
approximations made in Hückel theory for conjugated hydrocarbons:
- orbitals treated separately from s orbitals
- Only p orbitals treated in Hückel theory
- s orbitals treated as a rigid framework
- p orbitals expressed as linear combination of
carbon 2p orbitals (LCAO)
- All carbon atoms are treated as being identical
- All Coulomb integrals are set equal (Hrr = a)
- All overlap integrals between different AOs are set to zero (Srs = 0)
- All resonance integrals between adjacent carbon atoms set equal (Hrs
=b)
- All other resonance integrals set to zero
The
molecular orbitals of butadiene