The electrostatic potential and the average local ionization energy are valuable tools for understanding and predicting the reactivities of sites in nanomaterials such as graphene and carbon, B/N and B/C/N nanotubes, both pure, substituted and defective. These properties offer insight into the notable features of charge delocalization upon substitution and the effects upon reactivities when defects disrupt the carbon networks. We were the first to report the unusual electrostatic potentials of substituted (n,0) tubes, which display notably more facile charge delocalization than do other types. We have also shown that the average local ionization energy on the surfaces of defective nanotubes and graphene can prove to a reliable indicator of the relative reactivities of different sites of these systems. We are currently investigating the average local ionization energies on the molecular surfaces of a series of graphene model systems and nanotube caps, both with and without defects, to ascertain whether this property is able to predict not only the preferred first, but also second, hydrogenation and fluorination sites.