An ab initio study of the structure, tautomerism and molecular properties of the C- and N-amino-1,2,4-triazoles

The equilibrium structures of the 3-amino- and 5-amino-1H-1,2,4-triazoles and 4-amino-4H-1,2,4-triazoles, have been studied as a function of the conformation of the amino group in relation to the ring. The electric field gradients and dipole moments have been evaluated, again to assist experiment, where the complexity of the microwave spectrum through the presence of 4 14N quadrupolar nuclei, and low vapour pressure of the compounds has so far made spectral acquisition and interpretation impossible. The basis sets used were triple zeta C polarization, and the methodology was MP2. In order to determine the incremental effects on both structure and molecular properties when aza- and amino-substitution occurs in these five-membered heterocycles, the structures and molecular properties of the parent compounds 1H- and 4H-1,2,4-triazole have been obtained for comparison, using the same theoretical methods. The energy differences between tautomeric forms have been evaluated. Harmonic vibration frequencies have identified true minima, as well as some saddle points. q 2004 Elsevier B.V. All rights reserved.