Cubane octanitrocubane

Nitrocubanes are probably the most powerful explosives with a predicted detonation velocity of >10,000 ms-1. Cubanes were first synthesised at the University of Chicago, USA by Eaton and Cole in 1964. The US Army Armament Research Development Centre (ARDEC) then funded development into the formation of octanitrocubane [(ONC) (C8N8016)] and heptanitrocubane [(HpNC) (C8N7014)]. ONC and HpNC were successfully synthesised in 1997 and 2000 respectively by Eaton and co-workers. The basic structure of ONC is a cubane molecule where all the hydrogens have been replaced by nitro groups (1.6). HpNC is denser than ONC and predicted to be a more powerful, shock-insensitive explosive. 

The Hartree-Fock method has the advantage that it can be applied to relatively large molecules, e.g. octanitrocubane, with a reasonably good basis set, such as 6-31G. Since no electronic correlation is taken into account, Hartree-Fock calculations of heats of formation should be attempted only in conjunction with an isodesmic or homodesmic reaction [24]. If suitable ones are chosen, satisfactory results may be obtained [25,26]. On the other hand, an isodesmic reaction produced an HF/6-31G AHf of 166.1 kcal/mole for cubane, while a homodesmic one yielded 133.4 kcal/mole [25]. The experimental value is 148.7 kcal/mole [27], One must also be wary of a fortuitous element the same homodesmic reaction produced an excellent 149.7 kcal/mole with the very small STO-3G basis set [28]. 

The compact cage molecules, octanitrocubane and tetranitro tetraazacubane and diazadinitro tetrahedrane, have molecular strain energy locked-in which is released along with the internal combustion energy when they explode. The strain energies in these molecules are high as demonstrated in Table 4 for the case of cubane. 

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