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

Abstract

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 augcc-pVDZ basis sets coupled with Bader's theory of atoms in molecules. In the NO 2 group substituted molecules, the NZN bond distance increases with the increase of NO 2 groups, whereas in CZN bonds, this effect is relatively less, and the distances are almost equal. The topological analysis of electron density reveals that the electron density r bcp (r) of CZN and NZN bonds are significantly decreasing with the increase of NO 2 groups in the nitramine molecules. The Laplacian of electron density f 2 r bcp (r) of NZNO 2 bonds [DMNA: 2 16.7 eÅ 25 , MDA: 212.8 eÅ 25 and TNA: 27.9 eÅ 25 ] of the molecules are relatively less negative, and the values also decrease with the increase of NO 2 groups; this implies that the charge concentration decreases with the increase of NO 2 groups, which leads to weakening the NZN bonds of the molecules. The isosurface of molecular electrostatic potential displays high electronegative regions around the NO 2 groups. The oxygen balance OB 100 of the molecules increases as the number of NO 2 group increases in the molecules, in which, the TNA molecule having maximum OB 100 value [þ7.89]. The band gap, heat of detonation, bond dissociation energy and charge imbalance are predominantly depends on the number of NO 2 group present in the molecule. The charge imbalance parameter (n) has been calculated for all molecules, which reveals that TNA is a highly sensitive molecule, the corresponding n value is 0.047.

Estimating Grass–Soil Bioconcentration of Munitions Compounds from Molecular Structure

“…61,62,71 N-NO 2 is a highly electronegative group and it increases the potential reactive sites of these MCs. 72 Therefore, the fragment descriptor needs to be included.…”

“…A reason for these large underpredictions might be the absence of the nitramine (N-NO 2 ) functional group in the Absolv fragment descriptors set . Missing fragments has been identified as a major drawback for the group contribution approach in the estimation of solute descriptors. ,, N-NO 2 is a highly electronegative group and it increases the potential reactive sites of these MCs . Therefore, the fragment descriptor needs to be included.…”