# Why must there be degeneracy in the orbitals to have a Jahn-Teller effect? [closed]

Why is it the case that for Jahn-Teller effects to occur in transition metals there must be degeneracy in either the $$\mathrm{t_{2g}}$$ or $$\mathrm{e_g}$$ orbitals?

• Jahn-Teller effect is way broader than transition metals, or t2g, or eg. – Ivan Neretin Nov 15 '19 at 20:02
• What do you mean? But for transition metals there must be degeneracy – ChemEng Nov 15 '19 at 20:05
• I mean just what I said, Sure, there must be degeneracy in any case. But even when occurring in transition metals, Jahn-Teller effect is not restricted to t2g/eg thing. – Ivan Neretin Nov 15 '19 at 20:07
• A nice non-inorganic case of JT distortion, let me mention that, is that of cyclobutadiene: in its equilibrium structure (singlet state), it "escapes" antiaromaticity (and degenerancy) with asimmetry. The reason of JT distortion is pretty much the same in inorganic chemistry: an asymmetric (so, non-degenerate) state is energetically favoured compared to the degenerate and symmetric alternative – The_Vinz Nov 15 '19 at 20:24