Electromerism is a type of isomerism between a pair of molecules (electromers, electro-isomers) differing in the way electrons are distributed among the atoms and the connecting chemical bonds.
[1] In some literature electromerism is equated to valence tautomerism,[2] a term usually reserved for tautomerism involving reconnecting chemical bonds.
[3] One group of electromers are excited electronic states, but isomerism is usually limited to ground state molecules.
Another group of electromers are also called redox isomers: metal ions that can exchange their oxidation state with their ligands (see non-innocent ligand).
One of the first instances involved a cobalt(II)-quinone complex vs the related cobalt(III)-semiquinone species.