Aromaticity of bent benzene rings: A VBSCF study

Dijkstra, Fokke; Lenthe, Joop H. van

doi:10.1002/(sici)1097-461x(1999)74:2<213::aid-qua16>3.3.co;2-z

Cited by 4 publications

(4 citation statements)

References 7 publications

(7 reference statements)

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“…Table 1 lists the values obtained from local (HOMA, NICS, and PDI) aromaticity criteria for the 6-MR of the different pyramidalized pyracylenes. With respect to PDI, there is a small reduction of local aromaticity with an increase of the angle of distortion, in agreement with previous experimental [80][81][82][83][84] and theoretical results [85][86][87][88] on distorted aromatic rings. HOMA yields a similar trend with a slight deviation for θ = 10 and 20º.…”

Section: Some Reported Nics Drawbackssupporting

confidence: 91%

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: Some Reported Nics Drawbackssupporting

confidence: 91%

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

et al. 2010

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“…36 This agrees with the findings of some of us who confirmed that aromatic rings possess a significant degree of conformational flexibility. 37 It was shown that some deviations of the ring from planarity (with values of endocyclic torsion angles up to 30˚) do not prohibit cyclic π-electron delocalization.…”

Section: Distinguish I)supporting

confidence: 90%

Aromaticity in heterocyclic analogues of benzene: comprehensive analysis of structural aspects, electron delocalization and magnetic characteristics

Omelchenko

Шишкин

Gorb

et al. 2011

Phys. Chem. Chem. Phys.

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The degree of aromaticity of six-membered monoheterocycles with IV -VI group heteroatoms (C 6 H 5 X, where X=SiH, GeH, N, P, As, O + , S + , Se + ) was analyzed using the results of ab initio calculations at the MP2/cc-pvtz level. Values of common aromaticity indices including those based on electronic delocalization properties, structural-dynamic features and magnetic properties all indicate high aromaticity of all considered heterocycles.A decrease in aromaticity is observed with increasing atomic number of the heteroatom, except in the case of the pyrylium cation. However, not all types of indices or even different indices within the same type correlate well among each other. Ring currents have been obtained at the HF/cc-pvdz level using the ipsocentric formulation. Ring current maps indicate that in the case of cationic heterocycles the ring current persists in all molecules under consideration. The different conclusions reached depending on the type of index used, are a manifestation of the fact that when not dealing with hydrocarbons, aromaticity is illdefined. One should always express explicitly which property of the molecules is considered to establish a degree of "aromaticity".

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“…The three Dewar structures, shown in Figure 2, were not taken into account. Previous calculations [13,32] showed that they have a weight of about 6 -7% each. Because these weights are relatively small compared to the total weight of the Kekulé structures of about 80%, and because they obscure the view of the resonance of the latter structures, they were left out.…”

Section: Methodsmentioning

confidence: 99%

Valence bond descriptions of benzene and cyclobutadiene and their counterparts with localized bonds

Dijkstra

Lenthe

Havenith

et al. 2003

Int J of Quantum Chemistry

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Geometry optimizations have been performed for benzene and cyclobutadiene and for the corresponding moieties with nonresonating double bonds, viz. 1,3,5-cyclohexatriene and 1,3-cyclobutadiene. The calculations were done using the valence bond self-consistent field method including orbital optimization. Both strictly local and delocalized p-like orbitals were used for the system, which influences the strengths of the bonds. The calculations result in geometries and resonance and stabilization energies for benzene and cyclobutadiene, which are compared with theoretical models of aromaticity. The importance of resonance is discussed.

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Aromaticity of bent benzene rings: A VBSCF study

Cited by 4 publications

References 7 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

Aromaticity in heterocyclic analogues of benzene: comprehensive analysis of structural aspects, electron delocalization and magnetic characteristics

Valence bond descriptions of benzene and cyclobutadiene and their counterparts with localized bonds

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