Theoretical Description of Substituent Effects in 2,4-Pentanedione: AIM, NBO, and NMR Study

Abstract

The intramolecular hydrogen bond, molecular structure, and vibrational frequencies of 2,4-pentanedione and its seventeen derivatives have been investigated by means of density functional (DFT) method with 6-311++G** basis set. The nature of these interactions, known as resonance-assisted hydrogen bonds, has been discussed. The topological properties of the electron density distributions for O­H£O intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules (AIM). The results of calculations show that the Q-parameter describing the degree of ³-electron delocalization within the O=C­C=C­O­H keto­enol group correlates with the strength of the H-bond. Correlations between the H-bond strength and topological parameters have been also studied. Natural population analysis data, the electron density and Laplacian properties, as well as, ¯(O­H) and £(O­H) have been used to evaluate the hydrogenbonding interactions. Furthermore, calculated 1 H NMR chemical shifts (¤H) correlate well with the hydrogen-bond distance as well as electron density at the bond and ring critical points in the molecular electron density topography