On the experimental and theoretical calculations of rotameric conformations of a new Schiff base derived from amantadine

Abstract

Herein, the condensation of amantadine with the aldehyde piperonal resulted in a new Schiff base (1). This molecule was fully characterized by elementary analysis, infrared (IR), ultraviolet-visible (UV-Vis), 13C, 1H nuclear magnetic resonance (NMR) and high-resolution mass spectroscopy, logP (logarithm of partition coefficient), as well as single-crystal X-ray diffraction (SCXRD). The crystal structure crystallizes in the triclinic P1¯ space group with only one molecule of the Schiff base in the asymmetric unit, presenting the adamantane ring disordered over two positions. The crystal self-assembly is stabilized by weak interactions, such as analyzed by Hirshfeld surface. Using the DFT calculation, an energy barrier of 9.075 kcal.mol−1 was found between the two complementary conformations observed experimentally to the adamantane group. The computed infrared spectra (in vacuum and solution) are in good agreement with the experimental data. The energy of the HOMO orbitals was also calculated, in which energy values ​​range -7.4030–7.6027 eV, while LUMO orbitals are in the range of -0.3610–0.5717 eV, in which the polar solvents promoted greater stabilization in the border orbitals. The chemical potential (μ) from 3.467 to 3.520 eV indicate that the structure is stable. The magnitude of the chemical hardness (η) [6.934–7.041 eV] suggests the resistance to deformation of the electronic cloud over small electrostatic disturbances, showing that the system is not very polarizable. This result can be useful to further studies to investigate the coordination ability of compound 1 with hard metal ions.