Hydrogen bond studies in substituted imino-acetaldehyde oxime

The intramolecular hydrogen bond, molecular structure and vibrational frequencies of imino-acetaldehyde oxime and its twelve 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. As a geometrical indicator of a local aromaticity, the geometry-based HOMA index has been applied. Additionally the linear correlation coefficients between substituent constants and selected parameters in R position have been calculated. The results show that the hydrogen bond strength is mainly governed by the resonance variations inside the chelate ring induced by the substituent groups. The topological properties of the electron density distributions for OH⋯N intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules (AIMs). Furthermore, calculated 1H NMR chemical shifts (δH) 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. Finally, the natural population analysis method has been used to evaluate the hydrogen bonding interactions.