Molecular Structural Properties of [n]-Annulene (n = 8, 10, 12, 14) and its Boron Nitride Derivatives: Analysis of NMR, NBO, ELF and PDI

Abstract

Due to the importance of structural properties of annulene in physical and inorganic chemistry, the trajectory of the NBO to MO evolution can be written as natural atomic orbitals (NAO) → natural hybrid orbital (NHO) → natural bond orbital (NBO) → natural semi-localized MO (NLMO) → MO. The electron density distribution in this [n]-annulene series (both ions and molecules) (n = 8, 10, 12, 14) is investigated by NMR, NBO, ELF, FLU, and PDI analyses. The (4n+2)π and also 4nπ systems (Huckel’s rule) on variants of those compounds via the localized orbital localization (LOL) and electron localized function (ELF) are discussed, and a diatropic ring current (aromatic) is also distinguished for some other paratropic currents (anti-aromatic). The NHO direction and bond bending deviations from the line of nuclear centers are exhibited for understanding the situation of π and σ orbitals. In this work, for each NAO function, core, valence, or Rydberg, the orbital occupancy and the orbital energies are discussed. In addition, nucleus independent chemical shifts (NICSs) and statistical nucleus chemical shifts (S-NICSs) confirm the aromaticity and anti-aromaticity amounts in those rings.