HOMO/LUMO

Diagram of the HOMO and LUMO of a molecule. Each circle represents an electron in an orbital; when light of a high enough frequency is absorbed by an electron in the HOMO, it jumps to the LUMO.

HOMO and LUMO are acronyms for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The energy difference between the HOMO and LUMO is termed the HOMO–LUMO gap. HOMO and LUMO are sometimes referred to as frontier orbitals.^[1] The difference in energy between these two frontier orbitals can be used to predict the strength and stability of transition metal complexes, as well as the colors they produce in solution.^[2]

Roughly, the HOMO level is to organic semiconductors what the valence band maximum is to inorganic semiconductors and quantum dots. The same analogy exists between the LUMO level and the conduction band minimum.

In organometallic chemistry, the size of the LUMO lobe can help predict where addition to pi ligands will occur.

SOMO

A SOMO is a singly occupied molecular orbital such as half-filled HOMO of a radical.^[3]

See also

• Frontier molecular orbital theory
• Diels–Alder reaction
• Electron configuration
• Koopmans' theorem
• Ligand
• Organic semiconductor

References

1. ↑ GA Tech Chemistry p. 2-67 Frontier Orbitals
2. ↑ Griffith, J.S. and L.E. Orgel. "Ligand Field Theory". Q. Rev. Chem. Soc. 1957, 11, 381-383
3. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "SOMO".

External links

• OrbiMol Molecular orbital database