A recent study suggested the possibility that a particular isomer of N8O6 is metastable enough to be a high-energy-density material (HEDM). Using that molecule as a starting point, other molecules are considered as HEDM candidates. The molecules in the current study are variations of N8O6, varied in two ways. First, length increases are considered, with the insertion of additional rings of nitrogen in a "tube" structure. Also, changes in the "end-cap" of N8O6 are considered, since the NO3 "end-cap" is apparently the weakest site in the original N8O6 molecule. Stability with respect to bond breaking is determined by theoretical calculations of bond-breaking reactions. Hartree-Fock (HF) theory and perturbation theory (MP2 and MP4) are employed, along with the correlation-consistent basis sets of Dunning. Each molecule is examined to determine the lowest-energy pathway to dissociation. The major results are that a new end-cap can stabilize the molecule, but lengthening the "tube" structure actually weakens the molecule relative to N8O6.