The effect of the Coulombic potential energies in the origin of the axial-conformation preference in the 3-haloarsinan cations

In the past few decades, the origin of the axial-conformation preference in 3-haloarsinan cations (charge-dipole orientation effect), has been brought into question [halogen=F ( ), Cl (2), Br (3)]. In order to explore the source of the axial-conformation preferences in compounds 1-3, with G3MP2, LC-ωPBE and B3LYP technique and interpretations of natural bond orbital (NBO) we assessed the effect of the Coulombic electrostatic interactions, the hyperconjugative interactions, the electrostatic model associated with dipole-dipole interactions and the steric effects associated with the Pauli exchange type repulsions on the conformational properties of compounds 1-3. Natural Coulombic potential energies associated with attraction and repulsion between atoms that are adjacent or nonadjacent is in favor of the axial conformations of compounds 1-3. Between the axial- and equatorial-conformations the natural Coulombic potential energy distinction diminished from compound 1 to compound 3, this is justify their difference in corresponding total energy. From compound 1 to compound 3 through-space hyperconjugative interactions increase between the donor lone pairs of halogen atoms (LP3X) and the acceptor antibonding of H-As bonds [ ], X→ .Although, the electrostatic model correlated with the diversity of the total amount of dipole moments fails to account for rationalizing the conformational behaviors of compounds 1-3, the exploration of the dipole moments of the corresponding C-X and H-As bonds revealed that the variations of their four-center dipole-dipole interactions correlate well with their parallel conformational behaviors. The steric effects associated with the Pauli exchange type repulsions are in favor of the equatorial-conformations of compound 1-3.