Theoretical study on tetrazole and its derivatives. Part 7. ab initio MO and thermodynamic calculations on azido derivatives of tetrazole

Optimized molecular geometries and electronic structures for seven azidotetrazoles are obtained with ab initio MO method at HF/6-31G* level. The calculated results show that the tetrazole rings are planar and aromatic. The azido groups N-3 are approximately perpendicular to the cycles in the N-azidotetrazole neutrals and parallel to the cycles in the C-azidotetrazole neutrals and the anions. The molecular total energies and the frontier orbital energy gaps of the N-azidotetrazoles are larger than those of the C-azidotetrazoles. The 2H-azidotetrazole neutrals are more stable than the corresponding 1H-isomers. IR spectroscopy of the titled compounds is reported and, based on the scaled frequencies, their thermodynamic properties are calculated. In addition, temperature-dependent functions for heat capacities in the form (a + bT + cT(2)) in the 300 K-1000 K range are obtained. (C) 1999 Elsevier Science B.V. All rights reserved.