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1

The Relationship Between the Heats of Formation and the Molecular Electrostatic Potentials of Polyazaarenes

Bartošková M., Friedl Z.

Central European Journal of Energetic Materials

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2013

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Vol. 10, no. 1

103--112

EN

In order to characterize the explosive properties of high-nitrogen, energetic compounds, the heats of formation, either in the gas or the solid state, are often used as preliminary data. Their relationship to the number of nitrogen atoms involved is usually known, so exploring it cannot furnish any new information. However, the very promising, quantitative structure property relationship (QSPR) approach utilizes the molecular surface electrostatic potential V(r). We have therefore performed calculations for 12 azines and 10 azoles by the DFT B3PW91/cc-pVTZ method, and constructed their gas phase heats of formation Δf H°(298,g) by means of the isodesmic reaction approach. The acquired gas phase heats of formation Δf H°(298,g) were correlated with the molecular surface electrostatic potentials VS,max, VS,min, and VS(ring), which were calculated by the B3LYP/6-31G(d,p)//B3PW91/cc-pVTZ method. It is shown that the VS(ring) electrostatic potential describes very precisely the structures of high-nitrogen N-heteroaromatics, with both consecutive and isolated nitrogen atoms, and their thermodynamic properties.

2

Characterization of C-NO2 Bonds in Nitroaromatic Compounds: A Bond Disproportionation Approach

Pexa M., Friedl Z.

Central European Journal of Energetic Materials

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2010

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Vol. 7, nr 2

131-144

EN

Homolytic dissociation of C-NO2 bond represents the primary fssion process of nitroaromatic compounds under thermal, impact, shock and electric spark initiation stimuli. Homolytic bond dissociation energies BDE(C-NO2) describe the C-NO2 bond fssion. Theoretical calculations of BDEs are substantially infuenced by inadequate treatment of electron correlation. Recently the alternative method was suggested to overcome this substantial drawback – an isodesmic reaction RC-NO2 + SC-H → RC-H + SC-NO2 where SC-NO2 is standard nitroaromatic compound. This reaction is characterized by bond disproportionation energy DISP(C-NO2), which inherently cancels the electron correlation effect accompanying homolytic bond dissociation energies. The bond disproportionation energies DISP(C-NO2) and bond dissociation energies BDE(C-NO2) were evaluated for 11 nitro benzenes and 19 nitro toluenes at DFT B3LYP/6-311+G(d,p) level and correlated with their detonation velocities, D, and with charge of the most reactive nitro group, Q(NO2).

3

Accounts of the new aspects of nitromethane initiation reactivity

Zeman S., Atalar T., Friedl Z., Ju X-H.

Central European Journal of Energetic Materials

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2009

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Vol. 6, nr 1

119-133

EN

A well-known effect of amines, and also of water, on detonation characteristics of nitromethane (NM) is discussed from the point of view of the published knowledge about the study of initiation reactivity of this nitro paraffin. It is documented that bimolecular and higher interactions during the initiation of NM are impossible. The most widespread concepts of the primary steps of this initiation, i.e. formation of aci-NM anion [CH2=NO2]— by intermolecular hydrogen transfer in the neat NM submitted to shock and formation of this anion by action of an amine, have been scrutinized by the DFT B3LYP/cc-pVTZ+ method and evaluated as thermodynamically disadvantageous. Also the 1,3-intramolecular hydrogen shift in the NM molecule was characterized as a higher-barrier process. Two favorable primary mechanisms of fission in the NM initiation and development of its detonation were investigated by DFT B3LYP/cc-pVTZ+ calculations: homolysis of C–NO2 bond in the neat NM and homolysis of N–OH bond in its aci-form. The second mentioned pathway was found to be thermodynamically the most preferable mechanism of fission. Consequently, a detonation wave of NM with admixture of amine or water has a considerably reduced reaction zone length in comparison with the detonation of neat NM. The B3LYP/6-311++G(d,p) calculations of transition states revealed that an admixture of methylamine and/or water influences the conversion of nitromethane to its aci-form, and this effect is more feasible in the case of methylamine rather than water.

4

Electric Spark Sensitivity of Polynitro Arenes. Part II. Aspects of the Molecular Structure with Utilization of the Net Charges of Nitro Groups

Zeman S., Friedl Z., Kočí J.

Central European Journal of Energetic Materials

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2007

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Vol. 4, nr 4

23-31

EN

An ESZ KTTV instrument of a new, relatively simple construction has been applied to the determination of electric spark sensitivity (EES) of 31 polynitro arenes and their derivatives. Results obtained are compared with the theoretical DFT B3LYP/6-31G(d,p) Mulliken net charges of nitro groups, QNO2, which primarily react in the initiation by the spark. On the basis of analysis of the results obtained it is shown that intermolecular interaction plays in this initiation a considerable role. However, generally accepted presumption, that most positive QNO2 value represents a sensitivity of the given molecule, is not valid without reserve. If the polynitro aromatic molecule contains several potential reaction centres, the proper initiation might then be realized selectively (depending on the kind of initiation impulse).

5

Electric Spark Sensitivity of Nitramines. Part I. Aspects of Molecular Structure

Zeman S., Pelikán W., Majzlík J., Friedl Z., Kočí J.

Central European Journal of Energetic Materials

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2006

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Vol. 3, nr 3

27-44

EN

An ESZ KTTV instrument of a new, relatively simple construction has been applied to determination of electric spark sensitivity (EES) of 16 nitramines. Results obtained are compared with those from measurements by means of an older RDAD instrument. Attention was focused both on the relationships between the EES values from both the instruments and theoretical B3LYP/6-311+G(d,p) N-NO2 bond dissociation energies, B3LYP/6-31G(d,p) Mulliken net charges of the nitro group, heats of fusion and 15N NMR chemical shifts of the nitrogen atoms of the most reactive nitro groups, respectively. It is stated a larger difference between results of both instruments. The EES values from both the instruments correlate with such characteristics of molecular structure which correspond to the primarily leaving nitro group in the nitramine molecule. It has been found that these relationships for ESZ KTTV results are strongly affected by molecular structure factors. It is also pointed out that the dislocations in the crystals should have some relation to electric spark sensitivity.

6

Relationship Between Electronic Charges at Nitrogen Atoms of Nitro Groups and Onsets of Thermal Decomposition of Polynitro Arenes

Zeman S., Friedl Z.

Central European Journal of Energetic Materials

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2004

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Vol. 1, nr 1

3-21

EN

Thermal stability of twenty-five polynitro arenes has been examined by means of non-isothermal differential thermal analysis (DTA), and it was expressed as an onset of thermal decomposition, TD. Electronic charges, qN, at nitrogen atoms of the polynitro arene molecules were calculated by means of the ab initio DFT B3LYP/6-31G** method. The relationship was confirmed between the onsets TD and squares of the qN values for the nitro groups that are primarily split off. In the sense of this relationship, the compounds studied fall into five groups. The reason of this diversification and principle of the relationship existence are discussed. It is stated that stabilising influence of the crystal lattice of the studied polynitro arenes can be evaluated by DTA of solutions of these compounds in 1,3,5-trinitrobenzene (TNB).