LAUSR

Abstract The reaction between primary amine and aldehyde usually leads to a Schiff base. In this work, we present the results of research (NMR, ATR-FTIR, UV–Vis, and X-ray) of products obtained in the reaction of 5-methyl-3-aminoisoxazole (3AMI) or 3-methyl-5-aminoisoxazole (5AMI) with 17 different aldehydes. Based on the results, we prove that this simple and well-known reaction does not always leads to the obtaining of typical products. In addition, we present a discussion on tautomeric forms preferred by the investigated o‑hydroxy imine compounds in solution and in the solid state. Knowledge of the tautomeric form which given Schiff base exists in the solution and in the solid state is very important in the development of medicine and pharmacy as well as coordination chemistry.