Octanitrocubanes

Octanitrocubane (ONC), 10 742 Octanoic acid, physical properties, 5 29t Octanol, properties of commercial, 2 12t... 

Octanitrocubane (ONC) has a density of 1.979 g/cm, a calculated heat of formation of 594 kJ/mol, and a decomposition temperature above 200 °C. The explosive performance of octanitrocubane (41) from theoretical calculations is predicted to be exdemely high. The most recent theoretical estimate "" of VOD is 9900 m/s, making this compound one of the most powerful explosives synthesized to date. Surprisingly, the density of heptanitrocubane... 

More powerful and less shock sensitive explosives are continually being sought for both military and commercial use and work on octanitrocubane (ONC) [Structure (2.62)] is a meaningful step in this direction. ONC is a nitro derivative of... 

Octanitrocubane (ONC) is a white solid, somewhat soluble in hexane and readily soluble in polar organic solvents. The density of one of the ONC polymorphs is very high (1.979gcm"3) but is still lower than the calculated value (the latest and most sophisticated calculation predicts a density above 2.1 gem"3 for the most stable polymorph of ONC) which indicates the existence of a crystal form of ONC much more dense than that synthesized. Kamlet-Jacobs equations predicted that ONC is 15-30% better than HMX [109] (a most powerful currently employed military explosive) and 6% better (perhaps also less shock sensitive) than the recently discovered explosive HNIW [121, 253-258] or CL-20 as shown in Table 2.15. It is interesting to note that both HpNC and ONC have decomposition points well above 200 °C and are not detonated by hammer blows. 

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 The basic structure of ONC is a cubane molecule where all the hydrogens have been replaced by nitro groups (1.6).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. 

Shaw calculated the isokinetic point between homolysis and elimination as 770K for mononitro- and vicinal dinitro-alkanes and as 370K for gem-dinitro species [51]. In gem-polynitro species the C-N02 bond is weaker than in mononitro compounds due to inductive effects [52] thus, homolysis is thought to be the principal decomposition pathway in 2,2 dinitropropane and hexanitroethane [48]. Octanitrocubane has recently been synthesized (Fig. 6). Its crystal density was lower (1.979 g/cm3) than the predicted 2.1 [53]. Like hexanitrobenzene, octanitrocubane has a perfect oxygen balance, but at this point it appears unlikely that further development of this compound will be undertaken. 

Summary of MOLPAK + WMIN predictions for octanitrocubane with lattice energies (E, kcal mol 1) and densities (p, g cm 3) Gaussian 98 B3LYP/631G model with C2 symmetry... 

This has the additional advantage that reliable AHf will usually be available for the small molecules. On the other hand, a problem arises when the molecule of interest has two or more significant resonance structures, so that some of the bonds cannot be classified as single, double or triple benzene and nitro derivatives are obvious examples. Furthermore, as pointed out by Petersson et al [22], a relatively large molecule may require several of some of the smaller ones, so that the error in the latter is multiplied e.g., octanitrocubane would need 8 ethanes. Fishtik et al have suggested an alternative scheme, based on response reactions [23]. 

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]. 

Among the compounds in Table 2, by far the largest energy output in cal/g would be anticipated from octanitrocubane (ONC), 44, and its tetraazacounterpart, 45. ONC has recently been synthesized [116], after years of effort, and is expected to show excellent detonation performance... 

Fig. 1.7 Molecular structures of 5-nitro-l,2,4-triazol-3-one (NTO), 1,3,3-trinitroazetidine (TNAZ), hexanitrohexaazaisowurtzitane (CL-20), octanitrocubane (ONC) and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX).

Nitrogen-rich hetarenes have been evaluated favorably as energy-rich materials useful as explosives, rocket propellants and in pyrotechnics (08CHEC3-739). Most nitro derivatives or perchlorates have drawbacks for such uses, except perhaps for octanitrocubane. However, the aromatic... 

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