Topic 4: MO theory: Heteronuclear Diatomic & Ligand Group Orbitals

Question 1

HOMO and LUMO

Answer 1

Highest occupied molecular orbital
Lowest unoccupied molecular orbital

Question 2

2 orders of p orbitals (low to high)

Answer 2

sigma pz
pi (px, py)
pi* (px, py)
sigma* pz

pi (px, py)
sigma pz
pi* (px, py)
sigma* pz
due to flipping of orbitals

Question 3

Molecules where orbitals are flipped
Why?

Answer 3

N2 to O2 is where change occurs
The σ-π Crossover
The inversion in energy of the σ and π orbitals is due to the change in energy of the s and p orbitals that form them. When the s and p orbitals are of similar energy then extra mixing can occur if the symmetry is also correct

Question 4

back bonding/back donation

Answer 4

Where electrons interact to make bonds stronger (e.g. in ligand donation)