Moreover, the electron density at the BCPs is a good measure to evaluate the H-bond length and strength. Thus, there is correlation between the interaction energy and topological parameters at the BCPs [50]. The electron density decreases as a result of the elongation of the corresponding bond, while the opposite occurs when the bond length shortens. For instance, the H-bond length of O4…HO3-O3 in the conjugate base of L-fucose (formed from its deprotonation at C4-HO4) is 1.78 Å and the electron density at its BCPs is 0.0439 a.u., while the H-bond length of O1…HO2-O2 (formed from deprotonation of L-fucose at C1-HO1) is 1.97 Å and electron density at its BCPs decreases to 0.0289 a.u.. In addition, the values of electron density at BCPs of H-bonds in the conjugate bases of aldo-pentose decrease as intramolecular H-bond length increases. There is a good correlation between electron density, Laplacian of electron density, H-bond energy, sum of stabilization energy values, and intramolecular H-bond length in the conjugate bases of Deoxy-hexose sugars studied herein (stabilization energy will be explained in NBO analyses in the next section). Figure 4 presents the linear correlation between the values of\(\ \rho_{(r)}\), , andE(2) with bond length in conjugate bases of L-fucose. Figure 5 presents the linear correlation between electron density ,\(\text{\ ρ}_{(r)}\) (e/au3), at H-bond BCPs and interaction energyand stabilization energyE(2) in the conjugate bases of D-ribose.