Thermochemistry, Tautomerism, and Thermal Decomposition of 1,5-Diaminotetrazole: A High-Level ab Initio Study

Abstract

Thermochemistry, kinetics, and mechanism of thermal decomposition of 1,5-diaminotetrazole (DAT), a widely used "building block" of nitrogen-rich energetic compounds, were studied theoretically at a high and reliable level of theory (viz., using the explicitly correlated CCSD(T)-F12/aug-cc-pVTZ procedure). Quantum chemical calculations provided detailed insight into the thermolysis mechanism of DAT missing in the existing literature. Moreover, several contradictory assumptions on the mechanism and key intermediates of thermolysis were resolved. The unimolecular primary decomposition reactions of the seven isomers of DAT were studied in the gas phase and in the melt using a simplified model of the latter. The two-step reaction of N elimination from the diamino tautomer was found to be the primary decomposition process of DAT in the gas phase and melt. The effective Arrhenius parameters of this process were calculated to be E = 43.4 kcal mol and log( A/s) = 15.2 in a good agreement with the experimental values. Contrary to the existing literature data, all other decomposition channels of DAT isomers turned out to be kinetically unimportant. Apart from this, a new primary decomposition channel yielding N, cyanamide, and 1,1-diazene was found for some H-bonded dimers of DAT. We also determined a reliable and mutually consistent set of thermochemical values for DAT (Δ H = 74.5 ± 1.5 kcal·mol) by combining theoretically calculated (W1 multilevel procedure along with an isodesmic reaction) gas phase enthalpy of formation (Δ H = 100.7 ± 1.0 kcal·mol) and experimentally measured sublimation enthalpy (Δ H = 26.2 ± 0.5 kcal·mol).

How will quantum computers provide an industrially relevant computational advantage in quantum chemistry?

“…through the use of explicitly correlated methods. [61][62][63][64][163][164][165] Even though an exponential speedup of quantum chemical calculations is theoretically expected on quantum hardware, a significant obstacle to consider is the enormous prefactor to the polynomial runtime of quantum computational algorithms. This prefactor is partially due to the desired chemical accuracy requiring a long circuit decomposition in the gate-based model, but primarily it is due to the enormous overhead that faulttolerant error correcting codes require.…”

Transition-metal-mediated reduction and reversible double-cyclization of cyanuric triazide to an asymmetric bitetrazolate involving cleavage of the six-membered aromatic ring

“…57 Both DLPNO-CCSD(T) and CCSD(T)-F12 techniques have recently been shown to perform quite well for thermochemistry and kinetics of nitrogenrich heterocycles. [74][75][76][77] To account for the solvent effects, the free energies of solvation were calculated at the M06-2X/6-311++G(2df,p) level of theory using the polarized continuum model (PCM) 59 for isotropic media with 3 ¼ 7.4 corresponding to tetrahydrofuran solution used in all syntheses. We used the gasphase vibrational partition functions and single-point solvation energies for gas-phase optimized geometries, as was earlier benchmarked.…”

Thermal Stability of Bis-Tetrazole and Bis-Triazole Derivatives with Long Catenated Nitrogen Chains: Quantitative Insights from High-Level Quantum Chemical Calculations

“…Zero-point energies and thermal corrections to enthalpy and Gibbs free energy were computed at the same DFT level. Note that the M06-2X functional was shown to yield reliable geometries (and quite often even reasonable activation barriers) for various kinetic problems. ,,, All of the equilibrium and transition state structures were ascertained to be the minima and first-order saddle points on the PES. The nature of all localized transition states was verified using the intrinsic reaction coordinate procedure .…”

“…In contrast to few existing DFT studies, we performed high-level ab initio calculations at the CCSD­(T)-F12 level. Recently, we have demonstrated the ability of this methodology to predict accurate (within 1 kcal mol –1 ) and reliable thermochemistry and activation barriers for energetic materials, including those with a high nitrogen content. − …”