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 ox-amides acid 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 H-1 magneti c resonance, by which the Delta delta/DeltaT values could be directly relat ed with proton mobility. The molecular structure of two oxamides in the sol id state was determined by X-ray diffraction experiments: The results showe d 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.