The process

MO checklist

1. determine the molecular shape and identify the point group of the molecule
2. define the axial system and find all of the symmetry operations on the molecule
3. identify the chemical fragments and put them along the bottom of the diagram
4. determine the energy levels and symmetry labels of the fragment orbitals
5. combine fragment orbitals of the same symmetry, estimating their splitting energy and draw in the MO energy levels and MOs in pencil
6. determine the number of electrons in each fragment and hence the central MO region, add them to the diagram
7. identify if any MO mixing occurs, determine the mixed orbitals and shift their MO energy levels
8. use the MO checklist!