In a recent work, the simultaneous presence of the C 2 axis and σ v plane was suggested as essential to ST inversion, thus making C 2v the lowest symmetry point group of molecules breaking the Hund's multiplicity rule. Indeed, results on 2T-4N' in Fig. show that comparatively large and negative ∆E ST values can be achieved even in a system where the only symmetry element is the molecular plane, but where the non-complementary frontier orbitals do minimize the HOMO-LUMO exchange integral.