Experimental and theoretical studies on the structure and vibrational properties of nitropyrazoles

Rao, E. Nageswara; Ravi, P.; Tewari, Surya P.; Rao, S. Venugopal

doi:10.1016/j.molstruc.2013.03.038

Cited by 18 publications

(6 citation statements)

References 34 publications

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“…10,[13][14][15][16][17] Based on calculations and spectroscopic studies, the electrostatic potentials and frontier molecular orbital energies of simple mono-nitropyrazoles have been evaluated: the electron-withdrawing group NO 2 is found to lower the HOMO/LUMO energy gap and increase the reactivity of pyrazole compounds. 13 Studies of protonation constants for nitropyrazoles suggest that the effect of the nitro group on azole chemistry depends on its position on the ring: the effect is stronger if the nitro group is close to the N atom of the pyrazole ring. 13,14 Thermal decomposition studies (25-250 • C) of nitropyrazole compounds give their stability in the order 3 → 4 → 1-nitropyrazole >pyrazole.…”

Section: Introductionmentioning

confidence: 99%

“…13 Studies of protonation constants for nitropyrazoles suggest that the effect of the nitro group on azole chemistry depends on its position on the ring: the effect is stronger if the nitro group is close to the N atom of the pyrazole ring. 13,14 Thermal decomposition studies (25-250 • C) of nitropyrazole compounds give their stability in the order 3 → 4 → 1-nitropyrazole >pyrazole. 15 Using time-resolved pulsed photoacoustic spectroscopy to excite some of the resonant modes of compounds at different temperatures, NO 2 is observed as a major ground electronic state product and the same stability orders are found.…”

Section: Introductionmentioning

confidence: 99%

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Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

Yuan

Bernstein

2014

The Journal of Chemical Physics

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Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (<50 K) for all three systems. The vibrational temperature of the NO product from DNP is (3850 ± 50) K, 1350 K hotter than that of the two model species. Potential energy surface calculations at the CASSCF(12,8)/6-31+G(d) level illustrate that conical intersections plays an essential role in the decomposition mechanism. Electronically excited S2 nitropyraozles can nonradiatively relax to lower electronic states through (S2/S1)CI and (S1/S0)CI conical intersection and undergo a nitro-nitrite isomerization to generate NO product either in the S1 state or S0 state. In model systems, NO is generated in the S1 state, while in the energetic material DNP, NO is produced on the ground state surface, as the S1 decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

Yuan

Bernstein

2014

The Journal of Chemical Physics

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“…N -Nitropyrazole ( 86 ) is normally prepared by direct nitration of pyrazole. ,, With an improved oxygen balance of −78%, it has been considered for its energetic properties as a model compound for decomposition of nitroazoles. However, 86 has a predicted VoD of only 6800 m/s and P CJ = 189 kbar .…”

Section: Catenated Nitrogen Compoundsmentioning

confidence: 99%

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

2020

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The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N–N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N2 is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

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“…Nitropyrazole compounds have the potential to be excellent coformers of CL-20 due to their good detonation properties and low sensitivity. Their structure, 20 explosive properties, 21,22 and thermal decomposition 23,24 have been studied through experimental and theoretical methods. However, their effects on the sensitivity of CL-20 upon the formation of the intermolecular interactions are not yet fully understood.…”

Section: Introductionmentioning

confidence: 99%

“…Here, three kinds of nitropyrazole molecules were designed based on the different substituent positions and numbers in 4-nitropyrazole, which is the most stable nitropyrazole compound with one nitro group. 20 The molecular structure of 4-nitropyrazole is shown in Figure 1. The functional groups are methyl, amino, and nitro groups, which are popular groups in energetic materials.…”

Section: Introductionmentioning

confidence: 99%

Multimolecular Complexes of CL-20 with Nitropyrazole Derivatives: Geometric, Electronic Structure, and Stability

2019

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The multimolecular complexes formed between 2,4,6,8,10,12-hexanitro-2,4,6,6,8,10,12-hexaazaisowurtzitane (CL-20) and nitropyrazole compounds were investigated using B3LYP-D3/6-311G(d,p) and B97-3c methods. CL-20 in these complexes was surrounded by methyl, nitro, and amino derivatives of 4-nitropyrazole. The influence of substituents on the molecular electrostatic potential distribution of nitropyrazoles was investigated to figure out the potential electrostatic interaction sites. For the complex, the O···H hydrogen bond was popular in the intermolecular interactions, and dispersion interaction played an essential role, especially in C x /CL-20 multimolecular complexes. Trigger bond analysis showed that their strength increased upon the formation of intermolecular weak interactions. Nitro group charge calculations stated that the negative charge on almost all nitro groups showed a significant increase. Therefore, the sensitivity of CL-20 seemed to be lower than the original. In addition, the transfer of electron density between CL-20 and nitropyrzoles in complexes was investigated, revealing the influence of weak interactions on the electron density of CL-20.

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Experimental and theoretical studies on the structure and vibrational properties of nitropyrazoles

Cited by 18 publications

References 34 publications

Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

Azole energetic materials: Initial mechanisms for the energy release from electronical excited nitropyrazoles

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

Multimolecular Complexes of CL-20 with Nitropyrazole Derivatives: Geometric, Electronic Structure, and Stability

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