181. Studies of aromaticity by nuclear magnetic resonance spectroscopy. Part I. 2-Pyridones and related systems

Elvidge, J. A.; Jackman, L. M.

doi:10.1039/jr9610000859

Cited by 212 publications

(118 citation statements)

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“…Depending on the model used, an aromatic molecule may be one that is more stable, less reactive in some directions, has more nearly equal bond lengths, a greater magnetisability anisotropy, or a more negative central nucleus-independent chemical shift (NICS [10]), than is expected. In this respect, the proposal to define aromatic systems as exactly those that support a diatropic ring current [11,12] has the advantage that the theoretical determination of whether a system supports a ring current with a given sense is a yes/no decision, even though experimental detection of that current still rests on a model of 1 H NMR shifts [13] or magnetic susceptibility [4]. That proposal is followed here.…”

Section: Introductionmentioning

confidence: 99%

Ring-current aromaticity in triplet states of 4n π electron monocycles

Fowler

Steiner

Jenneskens

2003

Chemical Physics Letters

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The ipsocentric approach to orbital contributions to current density predicts that a triplet state of a 4n p-electron H€ u uckel monocycle should be aromatic, in the sense of supporting a diatropic ring current, and that this current should be carried by just four of the p electrons (three for n ¼ 1). The magnetic criterion of aromaticity is thus in agreement with BairdÕs classic energy-based prediction of aromatic stabilisation for these species.

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Section: Introductionmentioning

confidence: 99%

Ring-current aromaticity in triplet states of 4n π electron monocycles

Fowler

Steiner

Jenneskens

2003

Chemical Physics Letters

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“…derivatives are electron-rich heterocyclic systems which are generally considered to possess a substantial degree of aromatic character (1)(2)(3). These compounds undergo electrophilic substitution with ease at the 3-and the 5-positions, with substitution often, but by no means always, occurring preferentially at C-3 (4-7; see also ref.…”

mentioning

confidence: 99%

Isocarbostyrils. I. Electrophilic Substitution Reactions

Horning¹,

Lacasse²,

Muchowski³

1971

Can. J. Chem.

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The electrophilic substitution of N-alkylated isocarbostyrils was examined in considerable detail. Bromination, acylation, nitration, and acid-catalyzed condensation with formaldehyde occurred exclusively at C-4 under relatively mild conditions. The acylation of isocarbostyrils has heretofore not been reported.The bromination of 2-methyl-5-nitroisocarbostyril in aqueous acetic acid gave 2-methyl-3,4-dihydro-3-hydroxy-4-bromo-5-nitroisocarbostyril (7) of unknown stereochemistry, as the sole product. When heated above its melting point, 7 lost the elements of water to give the "normal" product of bromination 8.In aqueous acetic acid, excess bromine was shown to convert isocarbostyrils to the corresponding 3,4-dihydro-3-hydroxy-4,4-dibromo derivatives whose structures were supported by spectral and degradative evidence.

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“…Of the characteristic properties associated with conjugated systems, diamagnetic susceptibilities arising from π-electron ringcurrents [1][2][3][4] have been considered as one of the main diagnostics of aromaticity [5][6][7] -albeit a controversial one. [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.…”

Section: Introductionmentioning

confidence: 99%

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

Balaban¹,

Mallion²

2012

Croat. Chem. Acta

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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181. Studies of aromaticity by nuclear magnetic resonance spectroscopy. Part I. 2-Pyridones and related systems

Cited by 212 publications

References 0 publications

Ring-current aromaticity in triplet states of 4n π electron monocycles

Ring-current aromaticity in triplet states of 4n π electron monocycles

Isocarbostyrils. I. Electrophilic Substitution Reactions

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

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