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By M. Agostinha R. Matos, Joel F. Liebman (auth.), Tadeusz M. Krygowski, Michał K. Cyrański (eds.)

ISBN-10: 3540683291

ISBN-13: 9783540683292

ISBN-10: 3540683437

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ISBN-10: 3540863990

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Aromaticity is a thought that seemed within the mid-nineteenth century to distinguish among unsaturated hydrocarbons and officially unsaturated benzene [1–3]. on the finish of the 19th century it appeared that cyclicity was once an important for differentiation among the 2, yet firstly of the 20th century it became out that the above assumption was once now not right simply because cyclooctatetraene exhibited normal houses recognized for polyenes [4]. the basic estate of b- zene-like compounds, usually pointed out with fragrant compounds, was once low react- ity. as a result thermodynamic balance was once outlined as resonance power [5, 6] and used to be the 1st quantitative degree of aromaticity. Many theoretical ways have been proposed later to estimate this volume, and now the criterion is frequently thought of to be the main primary [7]. virtually whilst, magnetic susceptibility was once used to explain aromaticity [8, 9]. as a result, many options in accordance with magazine- tism have been constructed, essentially the most potent in overview of aromaticity being nucleus autonomous chemical shift (NICS) [10] or Fowler’s maps of ring currents [11]. The criterion served Schleyer as a foundation for a definition of aromat- ity: “Compounds which express considerably exalted diamagnetic susceptibility are fragrant. Cyclic delocalisation can also lead to bond size equalization, abn- mal chemical shifts and magnetic anisotropies, in addition to chemical and actual houses which replicate full of life stabilisation”[12].

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Beak P, Lee J-K, Zeigler JM (1978) J Org Chem 43: 1536 63. Ribeiro da Silva MDMC, Souza P, Pilcher G (1989) J Chem Thermodyn 21:173 64. Guthrie JP, Pike DC, Lee Y-C (1992) Can J Chem 70:1671 65. Abboud J-LM, Jimenez P, Roux MV, Turrión C, Lopez-Mardomingo C, Podosenin A, Rogers DW, Liebman JF (1995) J Phys Org Chem 8:15 66. Lebedeva ND, Masalitinova TN, Mon’yakova ON, Oleinikova TP (1980) J Org Chem USSR (Engl Transl) 16:226 67. Domalski ES, Hearing ED (1993) J Phys Chem Ref Data 22: 805 68. Chickos JS, Hesse DG, Liebman JF, Panshin SY (1988) J Org Chem 53:3424 69.

F. Liebman What About Iso-Species? It is now admitted that all of the benzoannelated species corresponded to annelation on a formal double bond of the five-membered ring of the single-ringed heterocycles. What is to be done about the so-called iso-species? Presumably the above de-benzoannelation difference quantities can be directly compared. We know of no analog to the first procedure involving CH3XYZCH3 species in that these would generally be biradicals and/or zwitterions. There are few enthalpy of formation data for such species – indeed, the only cases where the heterocycle, its generally assumed less stable “iso-analog,” and the one-ring species have been thermochemically investigated in the experimental literature are those of benzisoxazole (the value used above and to be used here was from solution phase studies), anthranil (XL) (see [70]), isoxazole [34], and isobenzofuran (XLI), where more precisely we are referring to the 1,3-diphenyl species for this last heterocycle [76].

Matos MAR, Miranda MS, Morais VMF, Liebman JF (2005) Mol Phys 103:221 52. Dávalos JZ, Flores H, Jiménez P, Notario R, Roux MV, Juaristi E, Hosmane RS, Liebman JF (1999) J Org Chem 64:9328 53. Pushkareva ZV, Kokoshko ZU (1946) Zh Obshch Khim 16:1269 54. Boldyrev BG, Postovskii IYa (1950) Zh Obshch Khimii 20:936 55. Steele WV, Chirico RD (1990) Thermodynamics and the hydrodeoxygenation of 2,3-benzofuran. Cooperative agreement no. FC22-83FE60149 (NIPEP-457). IIT Research Institute, NIPEP, Bartlesville 56.

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Aromaticity in heterocyclic compounds by M. Agostinha R. Matos, Joel F. Liebman (auth.), Tadeusz M. Krygowski, Michał K. Cyrański (eds.)

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