Abstrac t : 2-cyanobenzoic acids are very important compounds in several sciences, and it is because of this that studying their tautomeric equilibria is of great interest. Ring-chain tautomeric equilibria of 2-, 3-and 4-cyanobenzoic, 3benzyl-2-cyanobenzoic and 1-cyano-2-naphthoic acids were studied in gas phase by means of mass spectrometry (MS). Furthermore, evidences of ring-chain tautomerism of 2-cyanobenzoic acid were found in solution using 1 H and 13 C nuclear magnetic resonance and in solid phase by infrared spectroscopy.

ketoamides are versatile intermediates for the synthesis of several heterocycles and they are also relevant compounds in biological systems, with their tautomeric equilibria being a crucial aspect to be studied in order to understand their chemical and biological behaviour. Tautomeric equilibria of a series of -ketobutanamides were analyzed by means of 1 HNMR, determining that ketoamide and Z-enolamide are the main tautomeric species in solution, both presenting internal hydrogen bonds. Keto-enol equilibrium predominates over other possible tautomerisms (e.g. amide-imidol). The enol tautomer appears to be favoured by electron withdrawing substituents and non-protic solvents. Thermodynamic parameters H and S were determined in CDCl3 and DMSO-d6, showing that the keto-enol equilibria are exothermic and require a molecule order increase.