Valence-bond and Huckel molecular orbital diradicals - Alternant versus nonalternant effects

Two distinct classes of diradicals are examined and compared. Valence-bond diradicals are topologically enforced, whereas Huckel molecular orbital diradicals can undergo skeletal distortions and transform to a nonradical form and tend to gain or lose electrons to form stable polyions. Alternant hydrocarbon diradicals are nonpolar species and nonalternant hydrocarbon diradicals tend to be polar species and less prevalent.