Comparison with molecular surface electrostatic potential and thermal reactivity of nitramines

Molecular surface electrostatic potentials V_S(r) (ESP) of seventeen nitramines have been calculated. As a criterion of the imbalance between the maximum positive, V_S,max and minimum negative, V_S,min values of molecular surface electrostatic potentials their sum was derived and used as a new simple characteristic for ESPs-V_S,Σ. These V_S,Σ values have close relationships with the Arrhenius parameters, activation energy E_a and preexponent log A, of thermal decomposition of the nitramines studied. The correlation between the V_S,Σ values and heats of fusion of the nitramines studied is described. These findings suggested analyzing the physico-chemical behavior of the nitramine crystals during this decomposition; in this connection an investigation was carried out using isothermal thermogravimetry and scanning electron microscopy of thermally exposed crystals of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d] imidazole (sintering of its crystal surfaces), of β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (cracking of its crystals during β →δ transition) and of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane. The results suggest a need to study the pre-decomposition states on thermal decomposition of the nitramines' molecule's crystals.