Despite not originating from a single electron configuration in the SCF-MO picture, the Hund's rule violations are well-defined because the involved triplet and singlet states are the lowest excited states within their irreducible representation. Furthermore, in most cases the triplet and singlet states have similar linear combinations, making it easy to identify states with the same electron configuration. Natural transition orbitals (Figure ) exhibit the same features as the frontier MOs. While these molecules already exhibit double-bond delocalization in the conjugated perimeter, we have tried to apply the substitution strategy described in our previous work. However, this does not work as intended because the nodal structure of the MOs in the linear combination differ; some examples are included in Table .