High energy derivatives of Cubane

Is Cubane a really good explosives?

Quantitative evaluation of the potential of a candidate explosive before synthesis is very difficult. Currently, estimation of energetic properties relies on the empirically derived Kamlet and Jacobs equations:

In these equations the heat released by the decomposition, the number of moles of gas produced, and the molecular
weight of these gases are all critical factors. Density too is crucial. Obviously, the more molecules of a high-energy material that can be packed into the limited volume of a shell or rocket the better. Less obvious, but more important, density affects the detonation velocity of an explosive. This is a specialized "linear" rate of reaction that ranges from 5 to 10 km/s in explosives and affects the maximum detonation pressure, a direct measure of the power of an explosive. For a given explosive, the detonation pressure is proportional to the square of its density, so great effort is made to obtain the highest density form of any particular explosive.

Numerous nitro compounds are employed commonly as military and commercial explosives. There is a continuing search for more powerful and less shock-sensitive examples. Such materials are also sought as potentially useful fuels and propellants. Most interest is focused on high-density organic compounds that contain all of the elements needed for combustion to gaseous products in the absence of air. Nitrocubanes carrying five or more nitro groups contain enough oxygen to oxidize all constituent carbon and hydrogen atoms to gaseous CO, CO₂, or H₂O. Each of these, along with N₂, "explodes" from the solid to 12 gaseous molecules. The expansion from the dense solid to a lot of gas (much expanded by the released heat) produces the desired effect in propellants and explosives. ONC has a "perfect" oxygen balance and would produce (were the detonation completely efficient) eight molecules of carbon dioxide and four of dinitrogen. As ONC has no hydrogen, no water forms when it burns; when used as propellants such zero-hydrogen compounds leave little or no visible smoke (steam) in the plume behind the rocket; such "low-signature" rockets are difficult to track.

On application of the Kamlet and Jacobs equations led ARDEC to predict that octanitrocubane would be a very much better explosive (Table 1) than the classic C-nitro compound trinitrotoluene (TNT), perhaps 15±30% better than the nitramine HMX (the most powerful, commonly used military explosive), and at least competitive with (and perhaps less shock-sensitive than) the newest experimental explosive CL-20.