Sensitivities of Heterocyclic Nitro Derivatives

There is currently a great deal of interest, as potential energetic materials, in heterocyclic molecules containing two or more linked nitrogens. As always, a key consideration is the desire to achieve the lowest possible degree of sensitivity to unintentional external stimuli, such as shock or impact. 

While the presence of several linked nitrogens is frequently associated with instability and/or sensitivity [25], this is not always the case. For example, some derivatives of the tetraazapentalene 6, such as the tetranitrodibenzo isomers 7, have surprising stabilities [26]. In an earlier computational analysis [27], we found 6 to be significantly more stable than its isomer 8, despite the four linked nitrogens in the former. Our study revealed considerable delocalization of charge in 6, which may be a factor in its stability. 

It is well-established, through both experimental and computational evidence [28-34], that there is a degree of instability associated with the presence in a heterocyclic ring of linked doubly-coordinated nitrogens, as in 8. For example, the measured enthalpies of formation of 9 - 11 show 9 to be approximately 20 kcal/mole less stable than 10 and 11 [35]. The origin of this 

Another source of instability associated with several linked nitrogens may be kinetic. Indeed Storm et al have suggested that the considerably greater sensitivity of the picryl triazoles 14 and 16 compared to their isomers 15 and 17 can be attributed to the availability, in 14 and 16, of a relatively facile decomposition route, through the loss of N2 from the triazole portion of the molecule [39]. 

We have investigated this kinetic factor in the case of the nitrotriazole 18, which is known to be very sensitive to impact [40], in contrast for example to 

---