𝛽−Aminoacroleine; intramolecular hydrogen bond; NBO; AIM and harmonic oscillator model of aromaticity index (HOMA).
The characteristics of the intramolecular hydrogen bonding for a series of 19 different derivatives of 𝛽-aminoacroleine have been systematically analysed at the B3LYP/6-31G∗∗ level of theory. The topological properties of the electron density distributions for N-H$\cdots$O intramolecular bridges have been analysed by the Bader theory of atoms in molecules. The electron density (𝜌) and Laplacian (∇2 ρ) properties at critical points of the relevant bonds, estimated by AIM calculations, showed that N-H$\cdots$O have low and positive character (∇2 ρ > 0), consistent with electrostatic character of the hydrogen bond. The vibrational study of the hydrogen bonded systems showed negative (red) shifts for the 𝜈(N−H) stretching mode. The 𝜋-electron delocalization parameter (𝑄) as a geometrical indicator of a local aromaticity and the geometry-based HOMA have also been calculated. Furthermore, the analysis of hydrogen bond in this molecule and its derivatives by natural bond orbital (NBO) methods support the DFT results. The results of AIM and NBO analysis as well as 𝜈(N−H) were further used for estimation of the hydrogen bonding interactions and the forces driving their formation. The various correlations were found between geometrical, energetic and topological parameters. The substituent effect was also analysed and it was found that the strongest hydrogen bonds exist for N+(CH3)3 and Cl substituents while the weakest ones for COOCH3.