Energetic Tricyclic Polynitropyrazole and Its Salts: Proton-Locking Effect of Guanidium Cations

Abstract

An axisymmetric polynitro-pyrazole molecule, 3,5-di­(3,5-dinitropyrazol-4-yl)]-4-nitro-1H-pyrazole (5), and its salts (6–12) were prepared and fully characterized. These compounds not only show promising energetic properties but also show a unique tautomeric switch via combining different cations with the axisymmetric compound (5). Its salts (6–9) remain axisymmetric when the cations are potassium, ammonium, or amino-1,2,4-triazolium. However, when the cations are guanidiums, the salts (10–12) dramatically become asymmetric owing to the fixed proton. The introduction of guanidium cations breaks the tautomeric equilibrium by blocking the prototropic transformations and results in the switch-off effect to tautomerism. The structural constraints of 1H NMR and 13C NMR spectra provide strong evidence for the unusual structural constraint phenomenon. These stabilized asymmetric tautomers are very important from the point of molecular recognition, and this research may promote further developments in synthetic and isolation methodologies for novel bioactive pyrazole-based compounds.

Combining the most suitable energetic tetrazole and triazole moieties: synthesis and characterization of 5-(1-hydroxy-3-nitro-1,2,4-triazol-5-yl)-1-hydroxy-tetrazole and its nitrogen-rich ionic derivatives

“…Broadened singlets at 8.93 ppm (N H -NH 2 ) and 7.21 ppm (C-N H 2 ) and a sharp resonance at 4.65 ppm (N-N H 2 ) are characteristic for aminoguanidinium cations. 37 TAG protons for 7 can be assigned to two broad singlets at 8.61 ppm (N H -NH 2 ) and 5.68 ppm (N-N H 2 ). All compounds show three signals for the bis-heterocyclic moiety.…”

Pushing the Limit of Nitro Groups on a Pyrazole Ring with Energy-Stability Balance

“…Pyrazoles having an NH proton undergoes nonstoppable prototropic transformations. As a result, the free proton of the pyrazole ring is difficult to observe in 1 H NMR. − Interestingly, in the 1 H NMR spectrum of 5 , a peak at 13.7 ppm was assigned to the fixed proton of the pyrazole (Figure a). In addition, five characteristic peaks corresponding to the five carbon atoms are observed in the 13 C NMR (Figure b).…”

High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species

“…Tautomerism is a phenomenon common to several classes of N-containing aromatic heterocycles, exhibiting many intriguing aspects that are relevant in many areas, including crystal engineering, drug design, energetic materials, and coordination chemistry. , Of particular interest are compounds for which quasi-degenerate tautomers are possible because they can be switched between each other depending on the environment. , The N-rich system of 1 is potentially tautomeric. In Chart are reported the canonical tautomers of the neutral and singly protonated species.…”