An Aromaticity Scale Based on the Topological Analysis of the Electron Localization Function Including σ and π Contributions

Santos, Juan C.; Andrés, Juan; Aizman, Arie; Fuentealba, Patricio

doi:10.1021/ct0499276

Cited by 167 publications

(132 citation statements)

References 37 publications

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“…Chesnut and Bartolotti, and Santos et al [12,[19][20][21][22] The ELF is defined to have values between zero and one, and in regions where electrons are alone or form pairs of opposite spins, the Pauli principle has little influence on their behavior, and such regions have a low value of excess kinetic energy and a maximum in the ELF. [17,23] Conversely, ELF is small in the regions where Pauli repulsion is large, such as between electron pairs.…”

Section: Introductionmentioning

confidence: 99%

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

2008

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The pi contribution to the electron localization function (ELF) is used to compare 4npi- and (4n+2)pi-electron annulenes, with particular focus on the aromaticity of 4npi-electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all-carbon annulenes are set up: the span in the bifurcation values DeltaBV(ELF(pi)) should be small, ideally zero, and the bifurcation value for ring closure of the pi basin RCBV(ELF(pi)) should be high (> or = 0.7). On the basis of these criteria, nearly all 4npi-electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)pi-electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D4h and D8h symmetry, respectively, the RCBV(ELF(pi)) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of alpha- and beta-electrons.

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Section: Introductionmentioning

confidence: 99%

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

2008

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“…So far, most of the previous studies have focused on the S type structure. [24][25][26][27][28][29][30][31][32][33][34][35][36] However, it is found that both L and S types are stable with no imaginary frequency (except L2 structure which has one imaginary frequency) and the order of stability is S1 $ S2 > L1 > L2 at the CCSD(T)(full)/aug-cc-pVTZ level of theory. Details of total energy evaluations are in the Supporting Information.…”

Section: Resultsmentioning

confidence: 98%

“…Boldyrev and Wang experimentally observed Al 4 Li 3 À cluster and suggested it to be antiaromatic because a Al 4 4À ring in the Al 4 Li 3 À contains four electrons and has a non-equilateral shape. 24) In subsequent reports, arguments ensued concerning whether the compound is truly ''antiaromatic'' [24][25][26][27][28][29][30] or is actually ''netaromatic''. [31][32][33][34] Schleyer and Chen concluded that the Al 4 Li 3 À cluster is net-aromatic because its aromaticity dominates over antiaromaticity.…”

Section: Introductionmentioning

confidence: 99%

Structural Dependence of Magnetic Shielding Properties in Al<SUB>4</SUB>Li<SUB>4</SUB> Clusters

Lee

Han²,

Majumder

et al. 2008

Mater. Trans.

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This work demonstrates that the binding of Li atom plays an important role in the Al 4 Li 4 clusters, which changes the structure of the Al 4 ring and induces the distinct magnetic shielding properties depending on the position of Li atom. The Al 4 Li 4 cluster possesses both aromatic (S type) and antiaromatic (L type) isomers depending on the position of Li atom with an 8.74 kcal/mol energy difference at the singlet state. The bond length alternation (BLA) values and nucleus independent chemical shift analysis of each canonical molecular orbital (NICS-CMO) analyses show that S type isomers are aromatic and L type isomers are antiaromatic as the singlet low-lying states. A cyclic reaction pathway between L and S type isomers is mapped with five low-lying and five transition states including two intermediate states.

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“…Topological analyses of the electron localization function (ELF) [22], and in particular the -contribution, ELF  , can be used to directly link molecular electronic structure properties with (anti)aromaticity. This has been exploited by Santos et al, Malrieu et al, and us [23][24][25][26][27]. The ELF  describes the kinetic energy destabilization at position r due to Pauli repulsion between same-spin -electrons, and it takes values in the range 0 ≤ ELF  (r) ≤ 1.…”

Section: Introductionmentioning

confidence: 99%

On the Importance of Clar Structures of Polybenzenoid Hydrocarbons as Revealed by the π-Contribution to the Electron Localization Function

et al. 2010

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Abstract:The degree of -electron (de)localization and aromaticity of a series of polybenzenoid hydrocarbons (PBHs) has been analyzed through the π-contribution to the electron localization function (ELF π ), calculated at the B3LYP/6-311G(d,p) hybrid density functional theory level. The extent of -electron delocalization in the various hexagons of a PBH was determined through analysis of the bifurcation values of the ELF  basins (BV(ELF  )), the spans in the bifurcation values in each hexagon (ΔBV(ELF π )), and the ring-closure bifurcation values of the ELF π (RCBV(ELF π )). These computed results were compared to the qualitative description of local aromaticities of the different hexagons in terms of Clar structures with -sextets. Benzene, [18]annulene, and thirty two PBHs were analyzed at their equilibrium geometries, and benzene and triphenylene were also analyzed at bond length distorted structures. In general, the description of PBHs in terms of Clar valence structures is supported by the ELF  properties, although there are exceptions. For PBHs at their equilibrium geometries there is a clear sigmoidal relationship between the CC bond lengths and the amount of -electron (de)localization at these bonds, however, this relationship is lost for bond distorted geometries. In the latter cases, we specifically examined benzene in D 3h symmetric "1,3,5-cyclohexatriene" structures and triphenylene in eight different structures. From the distorted benzenes and triphenylenes it becomes clear OPEN ACCESSSymmetry 2010, 2 1654 that there is a distinct tendency for the -electron network to retain delocalization (aromaticity). The ELF  analysis thus reveals an antidistortive rather than a distortive behavior of the -electrons in these investigated compounds.

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An Aromaticity Scale Based on the Topological Analysis of the Electron Localization Function Including σ and π Contributions

Cited by 167 publications

References 37 publications

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

Structural Dependence of Magnetic Shielding Properties in Al<SUB>4</SUB>Li<SUB>4</SUB> Clusters

On the Importance of Clar Structures of Polybenzenoid Hydrocarbons as Revealed by the π-Contribution to the Electron Localization Function

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