Untitled

Bollini, C. G.; Giambiagi, Mario; Figueiredo, Aloysio Paiva de

doi:10.1023/a:1018844410832

Cited by 28 publications

(26 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Using the resonance theory and the valence bond theory, it has been proven that all resonance structures can be obtained from suitable combinations of these delocalization schemes. 31,32 The sum of all possible delocalization schemes, including those resulting from cyclic permutations, 25 gives rise to the n-center electron delocalization index, n-DI,…”

Section: ͑2͒mentioning

confidence: 99%

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Mandado

Graña

Pérez‐Juste

2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

The partition of the multicenter electron delocalization indices and the nucleus independent chemical shift indices into alpha and beta contributions in open-shell systems has been performed. In general it is shown that a full understanding of aromaticity in these systems cannot be achieved by restricting the calculations to the global properties but by dissecting these properties into alpha and beta terms. The 4n+2- and 4n-aromaticity rules for singlet and triplet annulenes, respectively, reduce to a general aromaticity rule when the alpha and beta terms are studied separately. This new rule allows us to extend the concept of conflicting aromaticities to radical systems that are simultaneously alpha-aromatic and beta-antiaromatic or vice versa. The existence of such systems is demonstrated here by means of multicenter electron delocalization indices and nucleus independent chemical shifts. Finally, the global aromatic/antiaromatic character of these radical systems is estimated by means of aromatic stabilization energy, which is shown to be either slightly positive or slightly negative, thus reflecting the small aromatic/antiaromatic character of these radicals and reinforcing the conclusions obtained with aromaticity indices.

show abstract

Section: ͑2͒mentioning

confidence: 99%

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Mandado

Graña

Pérez‐Juste

2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…The multicenter delocalization indices were formerly shown to be a powerful tool for characterizing three-center bonds [41][42][43][44][45] and at a later stage proposed as a measure of the multicenter π electron delocalization in cyclic aromatic hydrocarbons. [46][47][48] More recently, Bultinck et al [49][50][51][52][53][54][55] and Mandado et al [56][57][58][59][60] have extended the application of multicenter delocalization indices into the study of local and total aromaticity of polycyclic aromatic hydrocarbons, [49][50][51]53,54,56,57,59 aromaticity of heterocycles, 58 homoaromaticity, 52,55 and concerted reaction mechanisms. 60 In this work the multicenter delocalization analysis is shown to provide valuable quantitative information about the covalent metal-metal bonding and the multicenter bonding in different molecular fragments.…”

Section: -6) 26 Sandwich Structures Of [Al 4 Tial 4 ] 2-and Na[almentioning

confidence: 99%

Bonding Study in All-Metal Clusters Containing Al₄ Units

et al. 2007

View full text Add to dashboard Cite

The nature of the bonding of a series of gas-phase all-metal clusters containing the Al4 unit attached to an alkaline, alkaline earth, or transition metal is investigated at the DFT level using Mulliken, quantum theory of atoms in molecules (QTAIM), and Hirshfeld iterative (Hirshfeld-I) atomic partitionings. The characterization of ionic, covalent, and metallic bonds is done by means of charge polarization and multicenter electron delocalization. This Article uses for the first time Hirshfeld-I multicenter indices as well as Hirshfeld-I based atomic energy calculations. The QTAIM charges are in line with the electronegativity scale, whereas Hirshfeld-I calculations display deviations for transition metal clusters. The Mulliken charges fail to represent the charge polarization in alkaline metal clusters. The large ionic character of Li-Al and Na-Al bonds results in weak covalent bonds. On the contrary, scarcely ionic bonds (Be-Al, Cu-Al and Zn-Al) display stronger covalent bonds. These findings are in line with the topology of the electron density. The metallic character of these clusters is reflected in large 3-, 4- and 5-center electron delocalization, which is found for all the molecular fragments using the three atomic definitions. The previously reported magnetic inactivity (based on means of magnetic ring currents) of the pi system in the Al42- cluster contrasts with its large pi electron delocalization. However, it is shown that the different results not necessary contradict each other.

show abstract

“…The use of multicenter bond indices or n ‐center delocalization indices, n ‐DI's, as a measure of aromaticity in 5‐ and 6‐center rings was initially proposed by Giambiagi and coworkers 25–28. They interpreted all the possible valence structures of benzene, including those of Kekulé, in terms of 6‐center electron delocalization 27, 28. Because the n ‐DI measures the extension of the electron delocalization to n atoms, aromatic molecules are expected to display larger n ‐DI's than those of nonaromatic when they are computed for all atoms of the ring.…”

Section: Introductionmentioning

confidence: 99%

Chemical graph theory andn‐center electron delocalization indices: A study on polycyclic aromatic hydrocarbons

2007

View full text Add to dashboard Cite

Relations between aromaticity indices derived from chemical graph theory and those based on 6-center electron delocalization are investigated for a series of polybenzenoid hydrocarbons. Aromatic stabilization obtained by means of the effective scaled electron delocalization is highly correlated to the resonance energy, RE, obtained both from SCF MO calculations and conjugated ring circuits model. Local aromaticity of benzene rings is discussed using two different criteria, in one of them aromaticity is just given by the cyclic pi-electron conjugation of the ring, whereas terms involving more than one ring are also considered in the other one. Indices derived from chemical graph theory and those obtained from the 6-center electron delocalization give rise to the same local aromaticity. Moreover, 6-center electron delocalization provides more quantitative information.

show abstract

Untitled

Cited by 28 publications

References 13 publications

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Bonding Study in All-Metal Clusters Containing Al₄ Units

Chemical graph theory andn‐center electron delocalization indices: A study on polycyclic aromatic hydrocarbons

Contact Info

Product

Resources

About

Untitled

Cited by 28 publications

References 13 publications

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Aromaticity in spin-polarized systems: Can rings be simultaneously alpha aromatic and beta antiaromatic?

Bonding Study in All-Metal Clusters Containing Al4 Units

Chemical graph theory andn‐center electron delocalization indices: A study on polycyclic aromatic hydrocarbons

Contact Info

Product

Resources

About

Bonding Study in All-Metal Clusters Containing Al₄ Units