Electronic structures, intramolecular hydrogen bond interaction, and aromaticity of substituted 4-amino-3-penten-2-one in ground and electronic excited state

Abstract

The hydrogen bond strength, molecular structure, and several well-established indices of aromaticity have been evaluated for 4-amino-3-penten-2-one and its 20 derivatives by means of density functional theory (DFT) with 6-311++G** basis set in the gas phase and the water solution. Moreover, the excited-state properties of intramolecular hydrogen bonding (IHB) in these systems have been investigated theoretically using the time-dependent density functional theory (TD-DFT). The nature of IHB interaction has been explored by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point (BCP) using atoms-in-molecule (AIM) theory. Results of AIM calculations indicate that H···O bond possesses low ρ and positive ∇2ρ(r), which are in agreement with electrostatic character of the IHB, whereas N–H11 bond has covalent character (∇2ρ < 0). Furthermore, the analysis of hydrogen bond in this molecule and its derivatives by natural bond orbital (NBO) methods supports the DFT results. The various correlations are found between geometrical, energetic, and topological parameters. The substituent effect is also analyzed and it is found that the strongest/weakest hydrogen bonds exist for CF3/F substitutions.