Further insight into three center hydrogen bonding. Participation in tautomeric equilibria of heterocyclic amides

In this work the synthesis and characterization in solution and solid state of three heterocyclic oxamides and four amides capable of forming three center hydrogen bond (THB) interactions is described. The formation of THBs in solution was established and studied by multinuclear and VT 1H magnetic resonance, by which the ??/?T values could be directly related with proton mobility. The molecular structure of two oxamides in the solid state was determined by X-ray diffraction experiments. The results showed that amides with S(n)S(5)S(6) (n = 5, 6 for OMe and NO2 respectively) motifs were less prone to establish tautomeric equilibria in solution than those with the simpler S(n)S(5) motif.