Theoretical studies on the molecular electron densities and electrostatic potentials in azacubanes

Energetics and the charge distributions in azacubanes (C₈NH_8–) have been obtained using the ab initio Hartree–Fock, second-order Mø øller–Plesset perturbation theory and hybrid density functional methods. For diazacubane to hexaazacubane the lowest-energy conformers have nitrogen atoms occupying the face opposite corners of a cube. The topography of the molecular electrostatic potential and the electron density of azacubane conformers have been investigated. The electrostatic potential studies have shown that successive substitution of nitrogen instead of CH groups of cubane engenders smaller and more localized electron-rich regions around the nitrogens of a cube. Further the bond ellipticity and the electron density at the bond critical point of the X–N bonds (X=C or N) in a cubanoid increase from azacubane to octaazacubane. The heats of formation of azacubanes calculated by the isodesmic reaction approach using different levels of theory correlate well with the electron density at the bond critical point of X–N (X=C or N) bonds in a cubanoid.