Probing the effect of nitro groups in nitramine based energetic molecules: a DFT and charge density study

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The structure, electron density distribution, energetic and electrostatic properties of simple nitramine based energetic TMA, DMNA, MDA and TNA molecules were determined using density functional theory (B3LYP) with the 6-311G** and aug-cc-pVDZ basis sets coupled with Bader's theory of atoms in molecules. In the NO2 group substituted molecules, the N–N bond distance increases with the increase of NO2 groups, whereas in C–N bonds, this effect is relatively less, and the distances are almost equal. The topological analysis of electron density reveals that the electron density ρbcp(r) of C–N and N–N bonds are significantly decreasing with the increase of NO2 groups in the nitramine molecules. The Laplacian of electron density ▽2ρbcp(r) of N–NO2 bonds [DMNA: − 16.7 eÅ− 5, MDA: − 12.8 eÅ− 5 and TNA: − 7.9 eÅ− 5] of the molecules are relatively less negative, and the values also decrease with the increase of NO2 groups; this implies that the charge concentration decreases with the increase of NO2 groups, which leads to weakening the N–N bonds of the molecules. The isosurface of molecular electrostatic potential displays high electronegative regions around the NO2 groups. The oxygen balance OB100 of the molecules increases as the number of NO2 group increases in the molecules, in which, the TNA molecule having maximum OB100 value [+7.89]. The band gap, heat of detonation, bond dissociation energy and charge imbalance are predominantly depends on the number of NO2 group present in the molecule. The charge imbalance parameter (ν) has been calculated for all molecules, which reveals that TNA is a highly sensitive molecule, the corresponding ν value is 0.047.