Molecular Electronic Topology and Fragmentation Onset via Charge Partition Methods and Nuclear Fukui Functions

We investigated theoretically the ground state electronic structure and the onset of molecular fragmentation of 1,1-diamino-2,2-dinitroethylene (FOX-7) using density functional theory. The molecular charge density was analyzed via two partition methods: the distributed multipole analysis (DMA) and the deformed atoms in molecules (DAM). In this framework, the push-pull effect, hydrogen intra-molecular bonding and site acid-base properties of the molecule were discussed. Our analysis indicates that the molecular origin of the low measured impact sensitivity of FOX-7 is due to the magnitude of multipole values of the C−N bonds in the NO2 groups, the delocalized electrons over the central C−C bond and the hydrogen bonds. The onset of FOX-7 decomposition and acid-base properties were examined with the nuclear Fukui functions. The results support nitro to nitrite rearrangement and direct release of a NO2 as a possible initial step in FOX-7 decomposition process. The approach suggested is general and can be especially useful for very large molecules to examine in detail their electronic structure and to guide the search for the decomposition mechanisms.