The excited state reactivity for the closure of six membered rings relies on the orbital scheme depicted in Figure . Chemical substitution, in addition to shifting activation energies and displacing orbital densities as discussed above, might modify the nature of the MOs around the Fermi level. Variations in the chemical scaffold change the number of p-electrons in the system, tuning the orbital energies, and possibly modifying the C2 symmetry of the HOMO and/or LUMO. In these cases, the general scheme for 4n+2 p-electron systems resulting in the WH rules might not be applicable.