Theoretical insights into the nature of the semipolar bonds X-O (X = N, P)

Present research is focused on the nature and properties of N-O and P-O bonds in both simple Y3XO molecules (Y = H, F, Cl; X = N, O) and heterocyclic compounds (pyridine, pyridine-N-oxides, phosphorine and phosphorin-1-oxides). Theoretical study has been performed by quantum-chemical calculations with B3LYP/aug-cc-pVTZ method. For the equilibrium structures the electron density distribution was considered by means of topological analysis (QTAIM) as well as analysis in the framework NBO scheme. According to the analysis of both canonical molecular orbitals and NBO for all considered compounds the two pairs of p-orbitals centered on the X and O atoms overlap forms two X-O pi-bonds, which together with the X-O & USigma;-bonding allow us to consider X-O as triple bond with almost cylindrical symmetry. For the heterocyclic molecules the influence of the substituents and the nature of the heteroatom on the structure, chemical bonding and aromaticity is discussed. (C)& nbsp;2022 Elsevier B.V. All rights reserved.