The role of the long‐range exchange corrections in the description of electron delocalization in aromatic species

Abstract

In this article, we address the role of the long-range exchange corrections in description of the cyclic delocalization of electrons in aromatic systems at the density functional theory level. A test set of diversified monocyclic and polycyclic aromatics is used in benchmark calculations involving various exchange-correlation functionals. A special emphasis is given to the problem of local aromaticity in acenes, which has been a subject of long-standing debate in the literature. The presented results indicate that the noncorrected exchange-correlation functionals significantly overestimate cyclic delocalization of electrons in heteroaromatics and aromatic systems with fused rings, which in the case of acenes leads to conflicting local aromaticity predictions from different criteria. © 2017 Wiley Periodicals, Inc.

Electron Delocalization in Planar Metallacycles: Hückel or Möbius Aromatic?

“…On the other hand, electrostatic interactions with the copper cation (the natural charge on Cu is +1.308) and noticeable σ‐delocalization involving 3d x2‐y2 orbital and the lone‐pairs from heteroatoms (which seem to hold the structure in a plane) support delocalization of π‐electrons in both quasi‐rings. It is worth noting that, according to the π‐EDDB R and LCAO π‐MO‐based electron populations, only a half of the total number of π‐electrons in the heterocyclic quasi‐rings (6.076|e|) is delocalized, which gives on average 0.608|e| per each quasi‐ring member; for comparison, the corresponding values for furan and pyrrole are 0.503|e| and 0.724|e|, respectively . Interestingly, both quasi‐rings contain in total ten atoms and therefore, in accordance with Figure b, the maximum of number of electrons that can be delocalized through the π‐system of conjugated 2p z orbitals is 10.…”

A theoretical study of the properties of ninety‐two “aromatic” six‐membered rings including benzene, azines, phosphinines and azaphosphinines

“…Using RCP(H) (that we have multiplied by 1000 to have not too small values) as an aromaticity criteria the result is:…”

The electron density of delocalized bonds (EDDB) applied for quantifying aromaticity

“…21,22,[80][81][82][83] The aromaticity indices based on magnetic and structural criteria predict increasing aromaticity going from terminal to the central ring, while the electronic aromaticity indices like I Ring , PDI, or H RCP predict the opposite trend. 33,34,84 It has recently been demonstrated, however, that in the latter group of indices the results dramatically depend on the choice of the exchange-correlation functional at the DFT theory level and as such they are somewhat less reliable at least in the case of polyacenes. 84 In this context, the EDDB k index gives virtually the same predictions as HOMA and FLU (regardless of the level of the theory).…”

“…33,34,84 It has recently been demonstrated, however, that in the latter group of indices the results dramatically depend on the choice of the exchange-correlation functional at the DFT theory level and as such they are somewhat less reliable at least in the case of polyacenes. 84 In this context, the EDDB k index gives virtually the same predictions as HOMA and FLU (regardless of the level of the theory). Furthermore, even the qualitative comparison of the global EDDB(r) maps with the magnetically induced ring-current density maps from the ipsocentric approach 4,23,85 presented in Fig.…”