Insight into shock-induced chemical reaction from the perspective of ring strain and rotation of chemical bonds

Density functional theory BLYP/DNP and hyperhomodesmotic equations were employed to calculate ring strain energy, the bond dissociation energy of X-NO2 (X=C, N) and the charges on the nitro groups of several four-membered and six-membered heterocycle compounds. BLYP/DNP and LST/QST + CG method were also applied to calculate bond rotational energy of X-NO2 (X=C, N) of above mentioned compounds. It indicated that ring strain energy of four-membered heterocycle nitro compounds is apparently higher than that of six-membered heterocycle nitro compounds. Predictably, ring-opening reactions may preferentially occur for those compounds containing higher ring strain energy under shock. In addition, C-NO2 bonds in these compounds may rotate easier than N-NO2 bonds in response to the external shock. As for N-NO2 bonds in these compounds, they also respond to the external shock by the rotation of N-NO2 bonds, once to the saddle point of the rotational energy barrier, the whole molecule will become relaxed, N-NO2 bond becomes weaker and eventually leads to the breakage. When one -C=O, -C=NH or -NH2 group is introduced to the six-membered heterocycle, the charges on the nitro groups of the new compound decrease drastically, and ring strains increase remarkably. It can be predicted that the new compounds will be more sensitive to shock, and the viewpoint is confirmed by the experimental results of shock sensitivity (small scale gap test) of several explosives.