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How to calculate Hückel π orbitals

Select a conjugated structure and choose Object › Chemistry › Hückel π orbitals. Each π orbital is drawn with its energy; the HOMO, LUMO, gap and π energy are listed.

Steps

  1. Select a conjugated structure, for example benzene.

  2. Choose Main menu › Object › Chemistry › Hückel π orbitals.

  3. The energy levels are on the left and the selected orbital on the right, with warm and cool lobes for its two phases..

    Hückel π orbitals of benzene: the levels, the HOMO drawn on the ring, and its energy α + 1.000β.Hückel π orbitals of benzene: the levels, the HOMO drawn on the ring, and its energy α + 1.000β.

  4. Read the π electrons, HOMO, LUMO, HOMO-LUMO gap, Spin multiplicity and π energy.

Real orbital energies

  • Real orbital energies (eV): Calculate runs GFN2-xTB on the arbastro server, usually in a few seconds.
  • Real orbital energies, accurate (DFT): Calculate runs DFT on the arbastro server, usually in minutes. You can keep working.

Note

Simple Hückel theory counts π electrons only, neighbors only, and neglects overlap; β is negative, so α + β lies below α. Heteroatoms use Streitwieser's parameters. It is a teaching model, not a quantum-chemical calculation: square cyclobutadiene comes out a triplet here, while the real molecule distorts to a singlet rectangle.

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Last updated Nov 12, 2026