Ultrasound-based synthesis, SC-XRD, NMR, DFT, HSA of new Schiff bases derived from 2-aminopyridine: Experimental and theoretical studies

Abstract The present work is related to the rapid and efficient preparation of Schiff bases (1 and 2) by reaction of 2-aminopyridine derivatives with 3-ethoxysalicylaldehyde under ultrasonic irradiation. The advantages, of using ultrasonic irradiation, are short reaction time, high yield and the ability to carry out large scale reactions. After characterization by NMR spectroscopic technique and elemental analyses, the crystal structures of compounds were confirmed by single crystal X-ray analysis (SC-XRD). For further elaboration of non-covalent interactions in the stabilization of packing of molecules, Hirshfeld surface (HS) inspection was accomplished by using crystal explorer software. B3LYP/Def2-TZVP level of theory was used to calculate electronic and structural parameters of synthesized compounds. Optimized structures and calculated data showed good correlation with experimental ones. In addition, two models of keto and phenol tautomerism were studied by calculating thermodynamic parameters and molecular electrostatic potential. Results showed that there are both nucleophilic and electrophilic centers in keto form, while only nucleophilic center is present in phenol form.