|
||||||||||||||||||||||
|
||||||||||||||||||||||
Properties of nitrocubane: |
||||||||||||||||||||||
| Neither HpNC nor ONC is detonated by hammer blows! Both have decomposition points well above 200 C. Octanitrocubane sublimes unchanged at atmospheric pressure at 200 C. HpNC forms beautiful, colorless, solvent-free crystals when its solution in fuming nitric acid is diluted with sulphuric acid. Single- crystal X-ray analysis confirmed the assigned structure and provided an accurate density at 21 C of 2.028 g cm±3, impressively high for a C, H, N, O compound. Although octanitrocubane catches the imagination with its symmetry, heptanitrocubane currently is significantly easier to make than ONC. It is denser, and it may be a more powerful, shock-insensitive explosive than any now in use. |
||||||||||||||||||||||
 |
||||||||||||||||||||||
| The density of ONC is high, 1.979 g cm±3, but lower
than expected, as can be seen from the graph of predicted/observed nitrocubane densities (Fig. 3). Even a simple extrapolation from the observed X-ray densities of the other nitrocubanes leads to an expected value of 2.06 g cm±3. |
||||||||||||||||||||||
| Comparison of the molecular packing in HpNC (Fig.
1) with that in ONC (Fig. 4) helps to explain this anomaly. In contrast to HpNC, no nitro group in the ONC crystal is interleaved amongst nitro groups of a nearby molecule so as to directly approach the strongly electron-deficient carbons of the cubane frame. There are just 14 close interactions about each ONC molecule, and all of these are electrostatically repulsive O-O contacts between nitro groups of adjacent molecules. |
||||||||||||||||||||||
 |
 |
|||||||||||||||||||||
