1) Biradical 
A diradical in organic chemistry is a molecular species with two electrons occupying two degenerate molecular orbitals (MO). They are known by their higher reactivities and shorter lifetimes. In a broader definition diradicals are even-electron molecules that have one fewer bond than the number permitted by the standard rules of valence. If the el...
See biradical.
an atom or molecule having two unpaired electrons. Also calledCf. free radical.