AbstractModified neglect of diatomic overlap (MNDO) calculations have been used to investigate the ground state properties of the 130 nonfully boron‐nitrogenalternating isomers of pentaazapentaboraazulene (PAPBAZ), N5B5H8. The two most stable of these nonfully boron‐nitrogen‐alternating isomers, 1,2,3a, 5,7‐pentaaza‐3,4,6,8,8a‐pentaboraazulene, (1,2,3a, 5,7‐PAPBAZ) (3), and 1,3,3a,5,7‐PAPBAZ (4) have strongly exothermic heats of formation (−142.5 and −142.4 kcal/mol, respectively), while the two least stable isomers, 1,6,7,8,8a‐PAPBAZ (131) and 1,2,3,3a,8a‐PAPBAZ (132), are calculated to have endothermic heats of formation (+95.43 and +96.31 kcal/mol, respectively). Each isomer optimized as a slightly to extremely nonplanar molecule, but each remained a bicyclic system containing a seven‐membered ring fused to a five‐membered ring. Thus, no ring‐opened structures were observed. An empirical relationship between the heat of formation and the number, position, and type of homonuclear (NN or BB) bonds present in the molecules could be established, but as the heat of formation for the molecules became more positive, the relationship became less strong. A general trend of diminishing energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was observed as the heat of formation became more positive. In addition to a discussion of the structures of (3), (4), (131), and (132), the structures of 2,3a,4,6,8‐PAPBAZ (9), 2,3a,5,6,8‐PAPBAZ (11), 1,2,4,6,8‐PAPBAZ (15), 2,3a,4,7,8a‐PAPBAZ (19), 1,3a,4,5,8‐PAPBAZ (32), 1,2,3,5,7‐PAPBAZ (47), 1,3a,5,8,8a‐PAPBAZ (67), 1,3a,6,7,8a‐PAPBAZ (87), 3a,4,6,8,8a‐PAPBAZ (106), 1,2,3,5,6‐PAPBAZ (109), 1,2,3a,8,8a‐PAPBAZ (116), and 4,5,6,7,8‐PAPBAZ (130) are discussed in detail. Some of these molecules were chosen because they represent the minima and maxima, respectively, in heats of formation [(3), (4), (130), (131), and (132)], ionization potentials [(9) and (32)], differences in LUMO and HOMO energies [(106) and (32)], and dipole moments [(11) and (87)]. The remaining molecules were chosen because each represent the most stable system containing the following homonuclear chains: B‐B‐B (15), N‐N‐N (19),