What is… aromaticity: a critique of the concept of aromaticity—can it really be defined?

Stanger, Amnon

doi:10.1039/b816811c

Cited by 209 publications

(188 citation statements)

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“…Such a possibility was first discussed by Schleyer [65] in the case of organic compounds, and lately used extensively by Stanger [111,112,114]. Some of us [113] have also analyzed the possibility of using NICS profiles in the analysis of inorganic species.…”

Section: Nics Profiles As Aromaticity Criteria In Inorganic Clustersmentioning

confidence: 99%

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

et al. 2010

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Abstract:The lack of reference aromatic systems in the realm of inorganic aromatic compounds makes the evaluation of aromaticity in all-metal and semimetal clusters a difficult task. To date, calculation of nucleus-independent chemical shifts (NICS) has been the most widely used method to discuss aromaticity in these systems. In the first part of this work, we briefly review our previous studies, showing some pitfalls of the NICS indicator of aromaticity in organic molecules. Then, we refer to our study on the performance of some aromaticity indices in a series of 15 aromaticity tests, which can be used to analyze the advantages and drawbacks of aromaticity descriptors. It is shown that indices based on the study of electron delocalization are the most accurate among those analyzed in the series of proposed tests, while NICS(1) zz and NICS(0) πzz present the best behavior among NICS indices. In the second part, we discuss the use of NICS and electronic multicenter indices (MCI) in inorganic clusters. In particular, we evaluate the aromaticity of two series of all-metal and semimetal clusters with predictable aromaticity trends by means of NICS and MCI. Results show that the expected trends are generally better reproduced by MCI than NICS. It is concluded that NICS(0) π and NICS(0) πzz are the kind of NICS that perform the best among the different NICS indices analyzed for the studied series of inorganic compounds.

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Section: Nics Profiles As Aromaticity Criteria In Inorganic Clustersmentioning

confidence: 99%

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

et al. 2010

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“…6,7 Similar to other fundamental chemical properties such as charge, electronegativity, or bond order, aromaticity is not an observable one and it has to be defined by convention and measured by a relative scale. 8,9 Although aromaticity is a unique physical phenomenon, it is manifested in multiple ways. Some consequences of aromaticity are energetic stabilization as well as particular chemical reactivity, geometry, magnetic and electronic properties.…”

Section: Introductionmentioning

confidence: 99%

A universal scale of aromaticity for π‐organic compounds

Alonso

Herradón

2009

J Comput Chem

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Aromaticity is an essential concept in chemistry, invented to account for the stability, reactivity, molecular structure, and properties of many organic and inorganic compounds. In recent years, numerous methods to quantify aromaticity based on the energetic, magnetic, structural, and electronic properties of molecules have been proposed but none of them is universal. The inability of establishing a universal scale of aromaticity based on a single parameter is due to the multidimensional character of this phenomenon. Consequently, aromaticity analyses should be carried out by employing a set of aromaticity descriptors on the basis of different physical manifestations of aromaticity. Here, we report a universal scale of aromaticity for pi-organic compounds based on the Euclidean distance between neurons in a self-organizing map. The most widely used aromaticity indicators have been used as molecular descriptors, and so our approach provides the first scale of aromaticity which contains the energetic, magnetic, and structural aspects of this property. The method is applicable to a wide variety of unsaturated organic compounds and allows quantification of both aromaticity and antiaromaticity. Additionally, the position of a compound on the bidimensional map determinates immediately the following: (a) the group (aromatic, nonaromatic, or antiaromatic) to which the system belongs, (b) their degree of pi-electronic delocalization, and (c) the similarity in aromaticity/antiaromaticity between different compounds. This new scale of aromaticity is able to indicate the expected order of aromaticity of analogues of fulvene and heptafulvene, heteroaromatic species, substituted benzenes, and functionalized cyclopentadienyl compounds.

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“…1 Obviously, the attempts to quantify aromaticity are based on the properties that are universally accepted to be associated with aromaticity: energy, geometry, electron density (resonance) and magnetic. 2 Most of the studies that are related to the magnetic properties of aromaticity are computational. 3 Thus, the work of R. Mitchell stands out as a unique experimental method for the quantification of aromaticity.…”

Section: Introductionmentioning

confidence: 99%

Is (benzene)Cr(CO)₃ really more aromatic than benzene?

Stanger

2017

Can. J. Chem.

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(benzene)Cr(CO)3 was claimed to be more aromatic than benzene, based on the central 1H Me chemical shifts in dimethyldihydropyrene annulated to it. In this paper, several dihydropyrenes are computationally investigated. NICS-scan methods are used to assess the ring current properties, and NMR calculations are used for obtaining NMR chemical shifts. The parent and four benz-annulated dihydropyrenes show excellent agreement with the experimental results, reported by R. Mitchell in several papers. The effect of annulating the antiaromatic cyclobutadiene was shown to be larger than that of benzene and to change the type of ring currents; while benz-annulated dihydropyrenes maintain local 14-annulene and local benzenic ring currents, the cyclobutadiene-annulated dihydropyrenes show global (and local) ring currents. A NICS-scan study of (benzene)Cr(CO)3 and a NICS-XY-scan study of the (CO)3Cr(C6H4)-annulated to dihydropyrene show that the benzene in the Cr complex is at most aromatic as benzene, probably somewhat less. A detailed study of the 1H chemical shifts suggests that the experimental results were somewhat misinterpreted, and that (benzene)Cr(CO)3 is at most as aromatic as benzene.

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What is… aromaticity: a critique of the concept of aromaticity—can it really be defined?

Cited by 209 publications

References 56 publications

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A universal scale of aromaticity for π‐organic compounds

Is (benzene)Cr(CO)₃ really more aromatic than benzene?

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What is… aromaticity: a critique of the concept of aromaticity—can it really be defined?

Cited by 209 publications

References 56 publications

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

A universal scale of aromaticity for π‐organic compounds

Is (benzene)Cr(CO)3 really more aromatic than benzene?

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Is (benzene)Cr(CO)₃ really more aromatic than benzene?