Abstract The experimental and theoretical studies on asymmetrical Schiff base, salicylideneimino-ethylimino-pentan-2-one (SEIPO) were studied. The tautomerism of SEIPO was also studied by calculations using density functional theory (DFT). Two of the four tautomers were shown to coexist. Tautomerism and the effect of solvent on the tautomeric equilibria in the gas phase and in different solvents were studied. According to calculated results, L3, L4 tautomers are more stable than the L1, L2 tautomers. The 1H NMR spectra give the additional evidence for the coexistence of the tautomers keto-amine and enol-imine for SEIPO. UV–vis spectra of SEIPO were recorded in various organic solvents to check the dependence of tautomerism on solvent types. The theoretical calculations and spectroscopic results indicate that the intramolecular hydrogen bonding (IHB) strength of SEIPO is stronger than that in 4-amino-3-penten-2-one)APO(. In addition, natural atomic charges, global reactivity parameters, and HOMO–LUMO gaps have also been discussed.

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