The II-III phase transition, however, was shown to be driven by the formation of biradical species and is facilitated by increased mobility of the alkyl side chains during a melting process. At room temperature, the concentration of biradical cores is quite low, meaning the potential for spin-spin interaction is quite low. However, as the temperature increases through the II-III transition, the biradical concentration abruptly increases conducive to forming new spin-spin interactions . Typically, in molecules where the biradical ground state is dominant, the major packing motifs are either face-on dimer pairs when unhindered or ladder-like stacking when steric hinderance prevents the former. In both cases, the high spin centers (where the radical is most localized) will line up and, in some circumstances, form a pseudo σ-bond .