Molecular species having two unpaired electrons, in which at least two different electronic states with different multiplicities [electron-paired (@S05699@) or electron-unpaired (@T06503@)] can be identified, e.g. H2C·–CH2–C·H2 propane-1,3-diyl (trimethylene).
See also:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1333 [Terms] [Paper]