The 1H, 13C and 15N NMR study on 5-carboxymethyl-1,2,4-triazole and 5-oxo-1,2,4-triazine derivatives

The 5-carboxymethyl-1,2,4-triazole (1, 2, 3) and 5-oxo-1,2,4-triazine (4, 5, 6) derivatives were examined in solution by the H-1, C-13 and N-15 NMR including g-HSQC, g-HMBC 2D techniques and in the solid phase by C-13 CPMAS NMR. Molecular modelling shows that there is not enough space for free rotation of neighbouring substituents at C-3 and N-4 and the two rings, especially in 4-6, should be twisted with respect to the central heterocyclic system. The X-ray diffraction analysis of 2 and 5 evidenced that in the crystal of 2 the twist angles of 2-pyridyl and phenyl rings are 20.4 and 74.0 degrees whereas in 5 they are 51.6 and 80.5 degrees, respectively. Intramolecular hydrogen bonds (NHO)-H-1-O-...=C are formed in triazines 4-6 in solution and in the solid state; the (HO)-O-... distance in 5 is 2.079 Angstrom. (C) 2001 Elsevier Science B.V. All rights reserved.