Theoretical study on tetrazole and its derivatives (8) Ab initio study on nitramino derivatives of tetrazole

The fully optimized geometries and electronic structures of seven nitramino derivatives of tetrazole are calculated by ab initio method at HF/6 - 31G* level. The results show that the tetrazole ring is approximately planar. T he aromaticity for neutral 2H - tetrazoles is higher than that for the corr esponding 1H - isomers. The nitramino group in 5 - nitramino - 1H - tetrazo le is co - planar to the ring due to the hydrogen bonding between O(10) and H(11), whereas in others the nitramino groups are perpendicular to the rin g planes. The calculated energy results at different theoretical levels sho w that electron correlation effects in the title compounds are greater. The total energies of the neutral 1H tetrazoles are higher than those of the 2 H - isomers. Among three anions 5 - nitraminotetrazole anion is the most st able. The protonation sites and coordination modes of the title compounds a re elucidated based on the charge distribution. The IR spectra, thermodynam ic properties, i,e. standard molar enthalpy, standard molar heat capacity a nd standard molar entropy of the tide compounds are calculated. Finally, te mperature - dependent functions for heat capacities in the form( a + bT + c T(2)) in the 300K similar to 1000K range are obtained. Comparison shows tha t the title compounds have similar thermodynamic properties and as the temp erature rises, the difference between the thermodynamic functions of the ne utral species and the corresponding anions increases.