How Diradicaloid Is a Stable Diradical?

Splitting orbitals: By using an occupation-number scale, the extent to which observable diradicals are diradicaloid is quantified by calculations, and the factors controlling this character are discussed. A deeper understanding of how the stability of the singlet diradical is affected by ligand substitution (see picture) will help synthesize more stable singlet diradicals with controllable amounts of diradical character that bridge the regime between unstable, and thus unattainable "pure" diradicals, and normal closed-shell molecules.