Electromerism

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. Some metalloporphyrins exist as electromers.^[4][5] as well as a set without a metal.^[6]