Structural characterisation of 2,3-disubstituted pyrazines: NMR and X-ray crystallography

2-Formyl-3-aminopyrazine (1), 2-acetyl-3-aminopyrazine (2) and 2-benzoyl-3-aminopyrazine (3) have been studied by multinuclear magnetic resonance spectroscopy in solution and in solid state. Amino-imine tautomerism in such derivatives has been discussed on the basis of the calculated stabilities of the different tautomers by the hybrid B3LYP/6-31G** method. The crystalline structure of compound 3 has been solved, it belongs to the monoclinic P21/n space group, and shows supramolecular architectures involving N-H⋯O and N-H⋯N-pyrazine intermolecular hydrogen bonds.