Basicity of nitropyrazoles and their simultaneous spectrophotometric determination

Dumanović, D.; Ćirić, Janka; Muk, A.; Nikolić, Violeta N.

doi:10.1016/0039-9140(75)80176-7

Cited by 21 publications

(12 citation statements)

References 9 publications

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“…Since there is no experimental data for vertical excitation energies of nitropyrazole molecules published so far, the experimental UV-Vis absorption spectra of nitropyrazoles are taken to determine the accuracy of the CASSCF calculations. Vertical energies for the three materials and the related UV-Vis maximum absorption wavelength 14,33,34 are summarized in Table IV. As shown in Table IV, the vertical excitations calculated through CASSCF(12,8)/6-31+G(d) for the two lowest lying excited electronic states (S 1 and S 2 ) of 4-nitropyrazole are 4.16 eV and 4.78 eV, respectively.…”

Section: Theoretical Results and Discussionmentioning

confidence: 99%

“…As a valuable intermediate and first step for understanding such behavior for energetic DNP, several research groups have studied properties of pyrazoles with a single nitro group. 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.…”

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: Theoretical Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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“…Some analytical techniques, such as high performance liquid chromatography [2,7,11,12], spectrophotometry UV-Vis [13][14][15][16], micellar electrokinetic capillary chromatography [17], planar electrochromatography and highperformance thin-layer chromatography [18] have been previously employed for simultaneous determination of PAR, PRO and CAF. Commonly, these methods are complex, time-consuming, expensive, and often require the use of organic solvents.…”

Section: Introductionmentioning

confidence: 99%

Square‐wave Voltammetric Determination of Propyphenazone, Paracetamol, and Caffeine: Comparative Study between Batch Injection Analysis and Conventional Electrochemical Systems

Silva

França

et al. 2017

Electroanalysis

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In this work, the performance of two methods for simultaneous determination of propyphenazone (PRO), paracetamol (PAR), and caffeine (CAF) were compared. One is based on the use of a conventional electrochemical cell (steady‐state condition) and the other on the use of a batch injection analysis (BIA) cell; both systems were associated with square‐wave voltammetric detection (SWV). Three well separated (▵E ≥ 0.25 V) oxidation peaks were obtained for PRO, PAR, and CAF using 0.1 mol L−1 H2SO4 as electrolyte and a boron‐doped diamond (BDD) as working electrode. In addition, the electrochemical oxidation mechanism of PRO is being proposed for the first time. The average relative standard deviations of CB and BIA methods were 4.1 % and 3.1 %, respectively. The conventional system presented better limits of detection and the BIA system a significantly greater throughput (four times faster). Statistical comparison between the results obtained with both proposed methods and those obtained by chromatography was carried out and no significant differences were observed (95 % confidence level).

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“…3,4 The spectra of C-substituted nitropyrazoles (R = Aryl or NO2) contain a shoulder on the long-wave side of the band detected, 't while the spectra of amino-substituted nitropyrazoles exhibit two bands of approximately equal intensities with maxima in the regions of 260--290 and 340--410 nm. For example, in neutral media, this band is observed within 250 to 290 nm; in sulfuric acid, it is shifted by ~30 nm to the short-wave region; 4 and in solutions of NaOH, it is shifted by --40 nm to the long-wave region.…”

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confidence: 99%

Investigation of UV spectra of isomeric nitropyrazoles by the semiempirical AM1 (CI) method

et al. 1997

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The absorption bands in the UV spectra of isomeric nitropyrazoles were assigned by the calculations in the semiempirica[ AMI (CI) approximation. The long-wave absorption of nitropyrazoles is caused by n~x* and n0~rt* transitions. The charge-transfer band is the most intense. "me x--,x* transitions undergo a considerable bathochromic shift in the deprotonation. The first ionization potential (PI) of the 4-nitropyrazole anion was estimated from the empirical dependence of the energy of the excited z-state on PI of alkyl-substituted 4-nitropyrazoles. The PI of the 4-nitropyrazole anion is 3 eV lower than that of a neutral molecule. This is evidence for a substantial destabilization of the boundary x-orbital in the heterolytic cleavage of the N--H bond. The analysis of the UV and NMR spectra of 3(5)-nitropyrazole confirms the viewpoint that the 3-nitro tautomer predominates in solution.

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Basicity of nitropyrazoles and their simultaneous spectrophotometric determination

Cited by 21 publications

References 9 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

Square‐wave Voltammetric Determination of Propyphenazone, Paracetamol, and Caffeine: Comparative Study between Batch Injection Analysis and Conventional Electrochemical Systems

Investigation of UV spectra of isomeric nitropyrazoles by the semiempirical AM1 (CI) method

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