Seeking the most stable isomer of azahomocubanes

This study examines the stability and protonation properties of four potential azahomocubanes. Through high-level ab initio computations, we find that 9-azahomocubane is the most stable isomer, closely followed by 5-azahomocubane, 1-azahomocubane, and 2-azahomocubane. However, understanding the stability of the systems with a nitrogen atom incorporated into a highly constrained polycyclic environment extends beyond mere bond angles or hybridization considerations. Strain energy analysis reveals that azahomocubanes experience less strain compared to their carbon congeners. An exploration of multiple solvents shows that their impact on relative energies and geometries is negligible. On the other hand, among the four isomers, 2-azahomocubane exhibits the highest tendency for protonation. Basicity, as assessed through the minimum electrostatic potential, correlates well with protonation affinities. The stability and protonation properties of four potential azahomocubanes are examined.