The Jahn- Teller Theorem

Question 1

What is the Jahn Teller effect?

Answer 1

It is a distortion to remove degeneracy by making an orbital lower in energy and stabilising the complex

Question 2

When does the Jahn Teller effect occur?

Answer 2

It occurs when there is a degenerate group state or when electrons are unequally distributed among orbitals of the same energy
UNEVEN DISTRIBUTION IF E-
Also when there are two options for filling the orbitals and both have the same energy (degenerate)

Question 3

What distortion can occur with a regular octahedron?

Answer 3

Tetragonal distortion

Two of the 6 bond will be longer and weaker

Question 4

For which complexes is the Jahn Teller effect particular important?

Answer 4

Important for d4 and d9 as these involve the uneven occupation of the eg orbitals
This effect is larger because the dx2-y2 and dz2 orbitals point directly at the ligands

Question 5

Why is the Jahn Teller effect small for t2g orbitals

Answer 5

The effect is small as these orbitals point towards the ligands
Often ignored

Question 6

When is the Jahn Teller effect the largest?

Answer 6

When it involves the uneven distribution of electrons in the eg orbitals