Molecular species having two unpaired electrons, in which at least two different electronic states with different multiplicities [electron-paired (singlet state) or electron-unpaired (triplet state)] can be identified, e.g.
H2C·–CH2–C·H2 propane-1,3-diyl (trimethylene).
See also: biradical
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1333 (https://doi.org/10.1351/pac199567081307)