Electric and Magnetic Properties Computed for Valence Bond Structures:  Is There a Link between Pauling Resonance Energy and Ring Current?

Abstract

To establish the link between the aromaticity descriptors based on the Pauling resonance energy and the molecular properties, the electric (polarizability) and magnetic (magnetizability) field response properties have been calculated using the valence bond approach for various molecules and their individual Kekulé resonance structures. The results show that there is no direct relationship between the Pauling resonance energy and the properties; the response properties are weighted averages of the properties of the individual structures. According to the aromaticity criteria based on molecular properties, one-structure benzene would be aromatic; thus, concerning molecular properties, spin-coupled bonds do not behave like localized bonds in Lewis structures, with which they are usually associated.

The non-covalent nature of the molecular structure of the benzene molecule

“…The equilibrium geometry was optimized at the CASSCF (6,6) level with a cc-pVDZ 52 basis set, using the GAMESS (version May 2012) program. 53 Normal mode frequencies were also calculated to confirm the geometry as a minimum.…”

“…Despite the amount of collective time spent on this problem and all published studies concerning the subject, it is still possible to find disagreements in the scientific community regarding the origins of the properties of this class of compounds. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] One of the more recent disputes concerns the relative importance of the s and the p electrons to the properties of aromatic molecules. The idea that the benzene molecule owed its preference for the D 6h geometry to the s-frame resistance against distortion along the b 2u ''Kekule ´'' mode was developed and popularized by Shaik et al in a series of papers.…”

Graph–topological approach to magnetic properties of benzenoid hydrocarbons

“…Recently published reviews 2 cover most of this work, thus only the latest achievements should be mentioned now. Aromatic character was analyzed from the point of view of AIM 3 parameters, 4 pyrenophanes were chosen to describe the interplay of p-electron delocalization and strain, 5 the analysis of strain in free sextet-resonant benzenoid and their antisextet dualists, 6 application of summation of NICS (nucleus independent chemical shift) as a measure of the global measure of aromaticity, 7 the analysis of difference in stability of straight and kinked linear polyacenes, 8 the local aromatic character in large polyacene molecules 9 and other benzenoid hydrocarbons, 10 calculation of electron affinities of polycyclic aromatic hydrocarbons 11 and solvation energies of their radical anions, 12 currentdensity maps as probes of aromaticity while indicating the global and Clar p-rings in totally resonant polycyclic aromatic hydrocarbons, 13 partitioning of p-electrons in selected benzenoid hydrocarbons, 14 analysis of the relation between Pauling resonance energy and ring currents 15 and topological approaches to energetic and magnetic properties. 16 For about 50 years aromaticity has been considered as a collective phenomenon.…”

The Nature of the Chemical Bond from a Quantum Mechanical Interference Perspective

“…Benzene is among the most studied systems in chemistry. This emblematic molecule is an annulene composed of 6 carbon atoms displaced on a D 6h symmetric planar ring, and its geometric, electronic and magnetic properties are still reasons for scientific inquiry . From the energetic point of view, the molecule is more stable than their cyclic polyenes analogues.…”