The HF, MP2, and DFT structures of neutral (N 6 ) and monoprotonated (N 6 H + ) hexazine, nitrogen analogues of benzene, were discussed. For neutral N 6 , the extended geometry-based HOMED (harmonic oscillator model of electron delocalization) index, being a measure of π-electron delocalization, is close to that of benzene. Protonation of one N atom in planar N 6 has no important effect on the HOMED value. Contrary to benzene, planar N 6 H + does not lose its aromatic character. π-Electrons of the ring are not engaged in the formation of the NH bond. The proton affinity (PA) of N 6 seems to be considerably lower than that of benzene (by ca. 16kcalmol −1 at the G2 level), indicating great NN lone pairs repulsion and electron-withdrawing effects of the N-aza groups (ca. 12kcalmol −1 for each N atom).