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 1 H, 13 C and 15 N NMR including g-HSQC, g-HMBC 2D techniques and in the solid phase by 13 C 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° whereas in 5 they are 51.6 and 80.5°, respectively. Intramolecular hydrogen bonds N 1 H⋯OC are formed in triazines 4–6 in solution and in the solid state; the H⋯O distance in 5 is 2.079Å.