Further consideration of the chemical hardnesses and electronegativities of species also reveals a reasonable distribution of Lewis acidic and Lewis basic solvents with hard and moderate chemical hardnesses. The corresponding results are depicted in Fig. . Noteworthy, for aprotic and apolar solvents one can observe a gap between electronegativities χ = 2.5 -3.5 eV and chemical hardnesses η = 3 -6 eV. However, for electronegativities χ > 3.5 eV, a reasonable distribution of aprotic and apolar solvents can be observed. In addition, a significant linear ordering of chemical hardness values for η > 6.0 eV with increasing electronegativities has to be noticed. The corresponding protic and polar solvents include diethylether, 2-propanol, ethanol, ethylene glycol, tetrahydrofuran and morpholine in combination with the aprotic and apolar solvents cyclohexane, heptane, octane, methyl- outcomes. Hence, it can be concluded that the presence of hydrogen bonds strongly limits the applicability of the HSP approach. In consequence, one can also conclude that Eqn. ( ) remains valid for aprotic and apolar compounds and provides reasonable estimates for HSPs values in terms of DFT calculations.