Recent investigations of this effect have concerned cooperative variants in crystals and its relation to fullerenes and other icosahederal systems. Generating an avoided crossing, the pseudo version occurs in fluxional molecules and manifests in stereochemical non-rigidity of molecules and ions. One way to explain this effect mathematically involves the odd terms in the vibronic perturbation expansion. Experimental demonstration of this phenomenon is observed in UV-VIS absorbance spectra as split bands. Another important property of this theorem is its failure to predict directionality, which explains the shortening of z-axis ligands. The most paradigmatic example is in the form of six-coordinate copper (II ) complexes with three electrons 
Recent investigations of this effect have concerned cooperative variants in crystals and its relation to fullerenes and other icosahederal systems. Generating an avoided crossing, the pseudo version occurs in fluxional molecules and manifests in stereochemical non-rigidity of molecules and ions. One way to explain this effect mathematically involves the odd terms in the vibronic perturbation expansion. Experimental demonstration of this phenomenon is observed in UV-VIS absorbance spectra as split bands. Another important property of this theorem is its failure to predict directionality, which explains the shortening of z-axis ligands. The most paradigmatic example is in the form of six-coordinate copper (II ) complexes with three electrons in the two e-sub-g orbitals. For 10 points, name this doubly-eponymous theorem that describes the geometrical distortion of non-linear molecules with degenerate electronic ground states to lower the overall energy and symmetry of the complex.
Recent investigations of this effect have concerned cooperative variants in crystals and its relation to fullerenes and other icosahederal systems.
Jahn-Teller effect [or theorem; or distortion]