ABINITIO CALCULATIONS OF 10 CARBON NITROGEN CUBANOIDS

The results of a uniform set of ab initio quantum-chemical calculations for 10 carbon/nitrogen cubanoids are presented. There are 22 possible C/N cubanoids with formulas (CH)8-nNn, where 0 less-than-or-equal-to n less-than-or-equal-to 8. We give results for one cubanoid for each value of n; for n = 4 both the T(d) and C4v structures are discussed. The geometries were optimized on the RHF/6-31G*//RHF/6-31G* energy hypersurfaces, and the stationary points so obtained were characterized by vibrational analyses. The effect of electron correlation on the energies of these structures is examined via MP2/6-31G*//RHF/6-31G* theory. All 10 structures are predicted to be stable molecules, and the vibrational analyses indicate that their geometries are well-defined by the RHF/6-31G*// energy hypersurfaces. Heats of formation are predicted via appropriate isodesmic reactions. All the structures are found to have large positive DELTAH(f)'s. Perhaps the most interesting result obtained is that the high-energy content of the nitrogen-rich cubanoids is not primarily due to bond strain, but rather to the high-energy content of the NN single bond. Comparisons of the ab initio DELTAH(f) values with semiempirical AM1, PM3, and MNDO predictions are made. If they can be synthesized and have reasonable kinetic stability, the C/N cubanoids containing four or more nitrogen atoms are likely to bc important energetic materials. A brief discussion is given of the potential of these materials as propellants and explosives.