The charge of the Rh center is another possible descriptor for the reactivity trends, and it can provide insights about the electronic effects of the ligands. Although the oxidation state of the metal takes on only two values in the cat- alytic cycle in Figure , I and III, independently of the type of ligands, this quantity is not related to the charge of the Rh in each molecule. More precisely, atomic charges in molecules are not quantum mechanical observables, and cannot be obtained experimentally. Nonetheless, they can be defined with various approximate computational schemes and, although their values are different from scheme to scheme, comparing charges computed with the same scheme does provide useful qualitative information.