By definition, the lattice energy is the difference between the energies of the ions in the solid phase and the gas phase. This simple model assumes that the differences between enthalpies of sublimation (assumed ∼lattice energy) for various compounds are dominated by differences in enthalpies of melting (i.e. the enthalpy of vaporization is similar for these quinone-based and hydroquinone-based models). This assumption is reflected by including the added constant h in (5), which captures the approximated enthalpy of vaporization across the dataset.