CH3CH3 & CH3OH Higher Orbitals

From WikidChem

These slides show the Molecular Orbitals (MO) for ethane and methanol, using the United Atom Model, which treats the separate atoms as parts of a fragmented nucleus. These slides show the unoccupied higher MOs, starting with the Lowest Unoccupied Molecular Orbital (LUMO) on slide 31. The red highlighted lines near the top and middle of the slide indicate the specific unoccupied orbital being shown on the slide.

On slide 31, the center diagram, created from the Atom in a Box program, shows the 3dz^2 atomic orbital of a single Argon atom. An Argon atom has the same number of electron pairs (7) as ethane and methanol do. Thus the AOs of Argon are analogous in shape to the MOs of the two compounds, though the fragmented "nucleus" of the molecules will distort the shape of the MOs.

The colors in the diagram show a change in sign of psi squared, rather than a specific sign. The color differences between the AO and MOs don't really matter. You can see from the right-side diagrams the analogous lobes from Ar's AO to ethane and methanol's MOs.

Methanol's MO is more distorted than ethane's because of the unsymmetrical -OH group at the top. The electron density in the blue lobes are disproportionatly on the right lobe, because that lobe is closer to the oxygen and hydrogen nuclei, which are strongly attractive to the electrons.

The other slides in this series are similar, each comparing the AO of Ar to the MOs of ethane and methanol. They show how the United Atom Model draws parallels between the orbitals of an atom and the orbitals of a molecule.