Aromaticity electron localization function

In a pericyclic reaction, the electron density is spread among the bonds involved in the rearrangement (the reason for aromatic TSs). On the other hand, pseudopericyclic reactions are characterized by electron accumulations and depletions on different atoms. Hence, the electron distributions in the TSs are not uniform for the bonds involved in the rearrangement. Recently some of us [121,122] showed that since the electron localization function (ELF), which measures the excess of kinetic energy density due to the Pauli repulsion, accounts for the electron distribution, we could expect connected (delocalized) pictures of bonds in pericyclic reactions, while pseudopericyclic reactions would give rise to disconnected (localized) pictures. Thus, ELF proves to be a valuable tool to differentiate between both reaction mechanisms. 

The pair density description of aromaticity of the chalcogenophenes was calculated using the atoms-in-molecules (AIM) and electron localization function (ELF) methods, with both methods yielding equal results for the formally single C-C single bond but differing for almost all other bonds <2000CPF1(257)175>. The molecular parameters of the... 

Fig. 9 Electronic localization function (ELF) for benzene. Left. ELF = 0.85 iso-surface. Right. ELF = 0.66 iso-surfaces. The right iso-surface is cut on the front side for showing the complex topology the Carbon core basins sharply separate from the scalar ELF field. The aromatic ELF basin is clearly defined. Both in the high or lower ELF value iso-surface, no separation between Sigma and Pi basins can be found, which is a characteristic of delocalized bonds, similar to that shown in Fig. 11. All the molecular plots reporting ELF iso-surfaces or MPD are performed using the Xcrysden program [44]...

Shghtly earher than the appearance of NICS, attempts to construct numerical characteristics of the electron delocalization based on Bader s quantum theory of atoms in molecules (QTAIM) (1990MI) or electron localization function (ELF) (1990JCP5397) had begun. The most important for aromaticity description are electron sharing indices. For example, the delocalization index (DI) provides a value 6(A,B) which is the number of electrons delocalized or shared between atoms A and B. The next useful aromaticity... 

Chesnut, SdviSKsiviii) using the electron localization function (ELF) to measure aromaticity ... 

Chesnut and Bartolotti described the aromaticity of a series of substituted five-membered cyclopenta-dienyl systems using the electron localization function (ELF), which is defined for a single determinant wave function built from Hartree—Fock or Kohn—Sham orbitals as... 

With ab initio calculations at the HF level and by employing the concept of the electron localization function ELF, the authors established that the cyclote-traarsenide anion, [c-As4] , shows electron delocalization primarily through the lone pairs, and may consequently also be described as lone pair aromatic. 

Santos JC, Polo V, Andres J (2005) An electron localization function study of the trimerization of acetylene reaction mechanism and development of aromaticity. Chem Phys Lett 406 393-397... 

Chesnut, D. B. and Bartolotti, L. J. 2000. The electron localization function description of aromaticity in five-membered rings. Chem. Phys. 253 1-11. 

Santos, J. C. Andres, J. Aizman, A. Euentealba, P. An aromaticity scale based on the topological analysis of the electron localization function including o and it contributions. J. Chem. Theory. Comput. 2005,1, 83-86. 

Magnetic Criteria This has been the main characterization criterion for the aromatic molecules from the theoretical standpoint. There are various methods, which have been developed that can describe the magnetic properties for aromatic compounds. Some of them are, multiple aromaticity (simultaneous presence of o- and Jt-aromaticity) [15], mapping ring currents, aromatic ring current shielding (ARCS) [16], nuclear-independent chemical shift (NICS) [17], bifurcation analysis of the electron localization function (ELF) [18] and many more. For a comprehensive review of the various techniques and the developments in the field of aromaticity, the readers are referred to two volumes of Chemical Reviews that were edited by Professor P. v. R. Schleyer [1,11]. 

C Using the Electron Localization Function to Measure Aromaticity... 

Santos, J. C. Tiznado, W. Contreras, R. Fuentealba, P. Sigma-pi separation of the electron localization function and aromaticity. J. Chem. Phys. 2004,120,1670. 

Poater, J. Duran, M. Sol M. Sdvi, B. Theoretical evaluation of electron delocalization in aromatic molecules by means of atoms in molecules (AIM) and electron localization function (ELE) topological approaches. Chem. Rev. 2005,105, 3911. 

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