Why is Benzene Unique? Screening Magnetic Properties of C₆H₆Isomers

Abstract

Magnetic properties are commonly used to identify new aromatic molecules because it is generally believed that magnetization and energetic stability are correlated. To verify the potential correlation between the energy and magnetic response properties, we examined a set of 198 isomers of C H . The energy and magnetic properties of these molecules can be directly compared with no need to invoke any arbitrary reference state because the studied systems are all isomers. Benzene is the global minimum on the potential energy surface of C H , 35 kcal mol lower in energy than the second most stable isomer, fulvene. Unlike its electronic energy, isotropic magnetizability of benzene is slightly lower than the average magnetizability of its isomers. Altogether, 44 isomers of C H were identified to have more negative magnetic susceptibility than benzene but were between 67.0 to 168.6 kcal mol higher in energy than benzene. However, benzene is unique in two ways. Analyzing the paramagnetic contribution to the magnetic susceptibility as originally suggested by Bilde and Hansen (Mol. Phys., 1997, 92, 237) revealed that 53 molecules have lower paramagnetic susceptibility than benzene but among monocyclic systems benzene has the least paramagnetic susceptibility. Furthermore, benzene has the largest out-of-plane magnetic susceptibility that originates from the strongest ring current among all studied species.

Local aromaticity mapping in the vicinity of planar and nonplanar molecules

“…Despite some controversial views, it is generally accepted that the more negative NICS, the more aromatic character shows the studied system while the antiaromatic molecules are characterized by its positive values . In addition, instead of using Bq probe, some authors used 3 He nuclear magnetic shielding .…”

The symmetry principle of antiaromaticity

“…A good overview about the state of research on aromaticity including references to a selection of current reviews is given in the introduction of ref. 2 While the connection of some of these properties seems obvious, no concise connection between all in full generality could ever be established. Here we analyze the antithetical concept of antiaromaticity which was originally introduced by Breslow 3 and find an intimate symmetry relation between its defining properties that so far seems to have escaped the general attention.…”

Vorticity: Simplifying the analysis of the current density

“…However, there is not a formal relation of the magnetic induced ring currents with the stability of aromatic molecules. Moreover, the original definition of aromaticity states that it is a ground state property while the J ( r ) is a response property that involves magnetic excited states . Nevertheless, there are several studies that show a correlation between energy indices of aromaticity and magnetic response indices, although, this has only been established for main group rings.…”

“…Moreover, the original definition of aromaticity states that it is a ground state property while the J(r) is a response property that involves magnetic excited states. [28][29][30][31][32] Nevertheless, there are several studies that show a correlation between energy indices of aromaticity and magnetic response indices, [14,[33][34][35][36][37] although, this has only been established for main group rings. For metals, such correlation has not been found.…”