ANALYSIS OF LOCALIZED ORBITALS IN AZABORA DERIVATIVES OF [8] ANNULENE: IN THE VIEWPOINT OF AROMATICITY AND INDUCED RING CURRENTS

Abstract

The electron density distributions among a series of [8] annulene (both ions and molecules) and its azabora derivatives, including its ions [B_nN_nC_(8–2n) H₈ (n = 1, 2, 3, 4)], are investigated by NBO and NMR analyses. The (4n+2)π and 4nπ systems (Hückel′s Rule) in these compounds are discussed via the localized orbital localization and electron localized function. A diatropic ring current (aromatic) and paratropic current (anti-aromatic) are distinguished. The natural hybrid orbital (NHO) direction and bond bending deviations from the line of nuclear centers are exhibited for understanding the states of π and σ orbitals. For ${{\text{B}}_{2}}{{\text{N}}_{\text{2}}}{{\text{C}}_{4}}\text{H}_{8}^{2-}$, ${{\text{B}}_{\text{4}}}{{\text{N}}_{\text{4}}}\text{H}_{8}^{2-}$, and ${{\text{B}}_{\text{4}}}{{\text{N}}_{\text{4}}}\text{H}_{8}^{2+}$ NBO calculations reveal that these structures are the dominant Lewis structures. In this work, for each NAO functions (core, valence, or Rydberg) the orbital occupancy and the orbital energies are discussed. In addition, the nucleus-independent chemical shifts and statistical nucleus independent chemical shifts confirm the amounts of aromaticity and antiaromaticity in these rings.