Theoretical Charge density Proof of N–N weak bonds of RDX Energetic Molecule
The bond topological analysis of Cyclotrimethylene-trinitramine (RDX) energetic molecule has been carried out for the wave function obtained from the ab initio and DFT methods of quantum chemical calculations. The geometrical parameters of all bonds are compared with that of experimental reports. The inclusion of diffuse function in HF basis set levels makes the significant shift of bond critical point towards carbon atoms of C–N bonds. The heteroatomic bond density character is well understood from unequal C-cp and cp-N distances in all C–N bonds. For all the level of calculations, the maximum bond density was found for all N=O bonds, attributes the maximum potential energy V(r). The N–N bond properties are strongly depends upon the equilibrium bond length which clears from charge concentration in shorter N1–N4 bond and charge depletion found in longer N2–N5 and N3–N6 bonding regions. The bond topological analysis of all bonds in RDX molecule resulted that the N–N bond is the weakest among all the other bonds. The weakness of N2–N5 and N3–N6 bonds than N1–N4 bond of RDX has also been analyzed from energy density calculation from various level of theories as an alternate for Laplacian of electron density. From the analysis of CHELPG charges at the MP2 level, the N–N bonds of RDX appears to have a significant ionic nature which attributes strong hyperconjugation effect. The hyperconjugation effect of RDX, due to polarization of N–N bonds, is the additional proof of weak N–N bonds in RDX explosive. The isosurface electrostatic potential shows the electro positive and negative region in the molecule. A large negative potential found at the vicinity of oxygen atoms.
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