Aromaticity as a Cornerstone of Heterocyclic Chemistry

Balaban, Alexandrù T.; Oniciu, Daniela C.; Katritzky, Alan R.

doi:10.1021/cr0306790

Cited by 688 publications

(391 citation statements)

References 346 publications

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“…[8][9][10][11] However, because of the so-called multidimensional character of aromaticity, [12][13][14][15][16][17][18][19] a quantitative measure requires the presence of several attributes, and this complicates quantitative assessments of the concept. One should note, however, that this multidimensional character has been discussed mostly for conjugated heterocycles, [20][21][22] whilst the present paper is about benzenoid hydrocarbons. Furthermore, in addition to the global diamagnetic anisotropy, local π-electron ring-current intensities can be determined for each ring [1][2][3][4]8 of a conjugated network -in our case, a benzenoid system.…”

Section: Introductionmentioning

confidence: 95%

Correlations between Topological Ring-Currents, π-Electron Partitions, and Six-Centre Delocalisation Indices in Benzenoid Hydrocarbons

Balaban¹,

Mallion²

2012

Croat. Chem. Acta

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119

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Abstract. Comparison is made between three different indices that characterise the individual rings of a wide range of condensed benzenoid hydrocarbons. Two of these ("π-electron partitions" and the six-centre delocalisation-indices that have been called "Δ 6 -values") have been introduced only recently as potential indicators of what might be called "local aromaticity", whilst the third ("topological π-electron ringcurrents") was suggested as a possible discriminator in this regard nearly fifty years ago. Whilst linear correlations between ring currents and π-electron partitions within certain restricted classes of ring types are good (with correlation coefficients of up to 0.998), agreement between the two indices over all classes of ring types is poor. Predictions arising from a consideration of π-electron partitions and Δ 6 -values seem, on the other hand, to be in somewhat better accord. It is therefore concluded that, despite its superficially intuitive appeal, the ring-current index is out of step both with π-electron partitions and Δ 6 -values as a general indicator of so-called "local aromaticity". (doi: 10.5562/cca1846)

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Section: Introductionmentioning

confidence: 95%

Correlations between Topological Ring-Currents, π-Electron Partitions, and Six-Centre Delocalisation Indices in Benzenoid Hydrocarbons

Balaban¹,

Mallion²

2012

Croat. Chem. Acta

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119

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“…Because of regioselective reactivity, many N-oxide derivatives are used in the synthesis of a number of organic compounds [1][2][3][4][5][6][7]. Imidazole N-oxides act as precursors of biologically active molecules, transition metal chelating agents [8,9], and inhibitors of the release of interleukin-1, cytokine release, and protein kinase p38 [10,11].…”

Section: Introductionmentioning

confidence: 99%

Non-covalent interactions of N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives—a case of intramolecular N-oxide hydrogen bonds

et al. 2017

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The crystal structures of new N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives are reported. The results of X-ray diffraction showed the existence of intramolecular hydrogen bonding between carboxamide nitrogen donors and N-oxide oxygen acceptors. The use of Quantum Theory of Atoms in Molecules allowed its classification as a strong interaction, with energy about 10 kcal/mol, and of intermediate character between closed shell and shared bonds. Comparison of experimental data and quantum theoretical calculations indicated that a substituent attached to the phenyl ring in the para position influences the strength and geometry of the title hydrogen bonding. Stronger π-electronwithdrawing properties of the higher energy substituent of the intramolecular hydrogen bond are observed. Among other intermolecular contacts in the studied crystals are C-H…O/ C-H…N hydrogen bonds of imidazole carbon atoms and some π…π stacking interactions between aromatic molecular fragments. Their importance in stabilization of the crystal structure was confirmed by the results of Hirshfeld surface analysis.

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“…Aromatic molecules have distinct chemical, spectral, magnetic, geometric, and energetic properties. [2][3][4][5] Natural selection has resulted in the use of several aromatic networks in various "biochemicals" which enable life processes: (i) building blocks in storing genetic information (DNA and RNA nucleotide bases); (ii) 4 of the 20 natural amino acids, two of which are essential; (iii) porphyrins which first allow the fundamental reaction of photosynthesis to proceed thanks to the chlorophylls, converting carbon dioxide and water into organic compounds and oxygen, and which second allow "reverse" processes with cytochromes involved in electron transport and with hemoglobin carrying oxygen and carbon dioxide in blood; (iv) many coenzymes and vitamins; and (v) many plant and animal hormones such as estrogens. The list of industrially made aromatic compounds includes pharmaceuticals, pesticides, dyestuffs, polymers, etc.…”

Section: Introductionmentioning

confidence: 99%

Claromatic Carbon Nanostructures

Balaban

Klein

2009

J. Phys. Chem. C

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Eric Clar’s qualitative ideas for benzenoids are described in application to various novel nanostructures: graphene, edges in graphene, carbon nanotubes, carbon nanocones, and carbon nanotori. The specially singled out most highly aromatic species with Clar structures consisting entirely of aromatic sextets are proposed to be termed “claromatic”. Several such claromatic nanostructures are identified as manifesting special properties. A molecular structural “(h,k)” characterization for benzo/grapheneic nanostructures is shown to link up neatly with Clar’s ideas.

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Aromaticity as a Cornerstone of Heterocyclic Chemistry

Abstract: For Abstract see ChemInform Abstract in Full Text.

Cited by 688 publications

References 346 publications

Correlations between Topological Ring-Currents, π-Electron Partitions, and Six-Centre Delocalisation Indices in Benzenoid Hydrocarbons

Correlations between Topological Ring-Currents, π-Electron Partitions, and Six-Centre Delocalisation Indices in Benzenoid Hydrocarbons

Non-covalent interactions of N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives—a case of intramolecular N-oxide hydrogen bonds

Claromatic Carbon Nanostructures

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