Walsh diagram

Walsh Diagram of an HAH molecule.

Walsh diagrams, often called angular coordinate diagrams or correlation diagrams, are representations of calculated orbital binding energies of a molecule versus a distortion coordinate (bond angles), used for making quick predictions about the geometries of small molecules.[1][2] By plotting the change in molecular orbital levels of a molecule as a function of geometrical change, Walsh diagrams explain why molecules are more stable in certain spatial configurations (e.g. why water adopts a bent conformation).[3]

A major application of Walsh diagrams is to explain the regularity in structure observed for related molecules having identical numbers of valence electrons (e.g. why H2O and H2S look similar), and to account for how molecules alter their geometries as their number of electrons or spin state changes. Additionally, Walsh diagrams can be used to predict distortions of molecular geometry from knowledge of how the LUMO (Lowest Unoccupied Molecular Orbital) affects the HOMO (Highest Occupied Molecular Orbital) when the molecule experiences geometrical perturbation.

Walsh's rule for predicting shapes of molecules states that a molecule will adopt a structure that best provides the most stability for its HOMO. If a particular structural change does not perturb the HOMO, the closest occupied molecular orbital governs the preference for geometrical orientation.[4]

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "correlation diagram". doi:10.1351/goldbook.C01348
  2. ^ Miller Carrie S (2015). "Walsh Diagrams: Molecular Orbital and Structure Computational Chemistry Exercise for Physical Chemistry". Journal of Chemical Education. 92 (6): 1040–1043. doi:10.1021/ed500813d.
  3. ^ Chen, E.; Chang, T. (1998). "Walsh Diagram and the Linear Combination of Bond Orbital Method". Journal of Molecular Structure: THEOCHEM. 431 (1–2): 127–136. doi:10.1016/S0166-1280(97)00432-6.
  4. ^ Mulliken, R.S. (1955). "Structures of the Halogen Molecules and the Strength of Single Bonds". J. Am. Chem. Soc. 77 (4): 884–887. doi:10.1021/ja01609a020.