A quantum chemical calculation and a charge density analysis have been performed on the energetic molecule trinitrobenzene (TNB) to characterize its bond strength and to relate the bond topological parameters with the impact sensitivity. The optimized geometry of the molecule was calculated by the density functional method B3P86 with the basis set 6‐311G**. The bond topological analysis predicts a significantly low bond electron density (∼1770 e nm−3) as well as Laplacian of electron density (−1.67×106 e nm−5) for CN bonds. This low value of the Laplacian indicates, the charges of these bonds are highly depleted, which confirms that these are the weakest bonds in the molecule. The N=O bonds bear a high negative value of Laplacian, reflecting that the bond charges are highly concentrated. The isosurface of the molecular, electrostatic potential (ESP) shows large electronegative regions at the vicinity of NO2 groups. Further analysis of ESP in the bonding region allows predicting the impact sensitivity. A sound relationship has been found between the ESP at the mid point of the bonds and its bond charge depletion. The positive ESP at the mid points of highly charge depleted CNO2 bonds reveals that these bonds are the sensitive bonds in the molecule.
ABSTRACT:A high-level ab initio Hartree-Fock/Møller-Plesset 2 and density functional theory quantum chemical calculations were performed on p-chlorobenzaldehyde diperoxide energetic molecule to understand its bond topological, electrostatic, and energetic properties. The optimized molecular geometry for the basis set 6-311G** exhibit chair diperoxide ring and planar aromatic side rings. Although the diperoxide ring bear same type of side rings, surprisingly, both the rings are almost perpendicular to each other, and the dihedral angle is 96.1 . The MP2 method predicts the OAO bond distance as $1.466 Å . The charge density calculation reveals that the CAC bonds of chlorobenzaldehyde ring have rich electron density and the value is $2.14 e Å
À3. The maximum electron density of the OAO bonds does not lie along the internuclear axes; in view of this, a feeble density is noticed in the ring plane. The high negative values of laplacian of CAC bonds (approximately À22.4 e Å
À5) indicate the solidarity of these bonds, whereas it is found too small (approximately À1.8 e Å À5 for MP2 calculation) in OAO bonds that shows the existence of high degree of bond charge depletion. The energy density in all the CAC bonds are found to be uniform. A high electronegative potential region is found at the diperoxide ring which is expected to be a nucleophilic attack area. Among the bonds, the OAO bond charge is highly depleted and it also has high bond kinetic energy density; in consequence of this, the molecular cleavage is expected to happen across these bonds when the material expose to any external stimuli such as heat or pressure treatment.
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