Thematische Bibliographien / Aromaticita

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Auswahl der wissenschaftlichen Literatur zum Thema „Aromaticita“

Autor: Grafiati

Veröffentlicht am 28. Juni 2021

Zuletzt aktualisiert am 7. Februar 2022

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Zeitschriftenartikel zum Thema "Aromaticita"

Gore, P. H. "Aromaticity." Endeavour 11, no. 1 (1987): 54. http://dx.doi.org/10.1016/0160-9327(87)90182-7.

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Stojanović, Milovan, Jovana Aleksić, and Marija Baranac-Stojanović. "Singlet/Triplet State Anti/Aromaticity of CyclopentadienylCation: Sensitivity to Substituent Effect." Chemistry 3, no. 3 (2021): 765–82. http://dx.doi.org/10.3390/chemistry3030055.

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It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, we chose the singlet state antiaromatic cyclopentadienyl cation, antiaromaticity of which reverses to triplet state aromaticity, conforming to Baird’s rule. The extent of (anti)aromaticity was evaluated by using structural (HOMA), magnetic (NICS), energetic (ISE), and electronic (EDDBp) criteria. We find that the extent of triplet state aromaticity of monosubstituted cyclopentadienyl cations is weaker than the singlet state aromaticity of benzene and is, thus, slightly more sensitive to substituent effects. As an addition to the existing literature data, we also discuss substituent effects on singlet state antiaromaticity of cyclopentadienyl cation.

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Bernasconi, Claude F. "Proton transfers in aromatic systems: How aromatic is the transition state?" Pure and Applied Chemistry 81, no. 4 (2009): 649–65. http://dx.doi.org/10.1351/pac-con-08-08-27.

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The question as to what extent aromaticity in a reactant or product is expressed in the transition state of a reaction has only recently received serious attention. Inasmuch as aromaticity is related to resonance, one might expect that, in a reaction that leads to aromatic products, its development at the transition state should lag behind bond changes as is invariably the case for the development of resonance in reactions that lead to delocalized products. However, recent experimental and computational studies on proton transfers from carbon acids suggest the opposite behavior, i.e., the development of aromaticity at the transition state is more advanced than the proton transfer. The evidence for this claim is based on the determination of intrinsic barriers that show a decrease with increasing aromaticity. According to the Principle of Nonperfect Synchronization (PNS), this decrease in the intrinsic barrier implies a disproportionately large amount of aromatic stabilization of the transition state. Additional evidence for the high degree of transition state aromaticity comes from the calculation of aromaticity indices such as HOMA, NICS, and the Bird Index. Possible reasons why the degree to which aromaticity and resonance are expressed at the transition state is different are discussed.

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Zong, He-Hou, Chuang Yao, Chang Q. Sun, Jian-Guo Zhang, and Lei Zhang. "Structure and Stability of Aromatic Nitrogen Heterocycles Used in the Field of Energetic Materials." Molecules 25, no. 14 (2020): 3232. http://dx.doi.org/10.3390/molecules25143232.

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Understanding the stabilization of nitrogen heterocycles is critical in the field of energetic materials and calls for innovative knowledge of nitrogen aromatics. Herewith, we report for the first time that nitrogen lone pair electron (NLPE) delocalization in five-membered nitrogen heterocycles creates a second σ-aromaticity in addition to the prototypical π-aromaticity. The NLPE delocalization and the attendant dual-aromaticity are enhanced as more carbon atoms in the ring are substituted by unsaturated nitrogen atoms. The presence of adjacent nitrogen atoms in the ring can enhance the aromaticity of the nitrogen heterocycles and improve in-crystal intermolecular binding strength but will decrease the firmness of the individual molecular architecture. Notably, such σ-aromaticity is not present in six-membered nitrogen heterocycles, probably due to the longer bonds and broader regions of their rings; therefore, six-membered heterocycles present overall lower aromaticity than five-membered heterocycles. This work brings new knowledge to nitrogen aromatics and is expected to inspire broad interest in the chemistry community.

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Yun, Bi Xiao, and Ablikim Kerim. "A study on the aromaticity and ring currents of dithienopyridines and dithienobenzene." Journal of Theoretical and Computational Chemistry 17, no. 01 (2018): 1850006. http://dx.doi.org/10.1142/s0219633618500062.

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The global aromaticity of dithienopyridine and dithienobenzene isomers was investigated using the topological resonance energy (TRE) and percentage topological resonance energy (%TRE) methods. The effect of variations in the positions of sulfur and nitrogen atoms on [Formula: see text]-electron delocalization is analyzed. The local aromaticity of these isomers is described based on the bond resonance energy (BRE) and circuit resonance energy (CRE) methods. Our BRE and CRE results show that structure of the central six-membered rings has a strong effect on global aromaticity. The aromaticity of these dithienopyridine isomers is enhanced when a complete pyridine unit exists in their middle ring structure, while the aromaticity of the dithienobenzene isomers is enhanced when a complete benzene unit exists in their middle ring structure. For dithienopyridines, our results obtained using the TRE method correlate well with the Bird aromaticity index as reported in the literature. Our ring-current results show that all these compounds are diatropic systems.

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Kalpana, Padmanaban, and Lakshminarayanan Akilandeswari. "Can Aromaticity of Fused Aromatic Ring in 1,3-Pentadiene Modulate its Reactivity towards [1,5]-Halo Shift? - A DFT Study." Asian Journal of Chemistry 33, no. 2 (2021): 447–52. http://dx.doi.org/10.14233/ajchem.2021.23092.

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In (Z)-1,3-pentadienes, [1,5]-H migration is suprafacially allowed while fluorine shift in this system takes place by a Contra Hoffmann antarafacial pathway for which aromaticity is the driving force. If aromaticity of the transition structure (TS) can drive a reaction towards a disallowed pathway as found in the case of fluorine, the role of aromatic ring annealed to (Z)-1,3-pentadienes in determining the reaction pathway and barrier is worth noting. Hence, the combined role of aromaticity of transition state and the loss in aromaticity of the annealed ring has been explored during the [1,5]-X (X = H, F, Cl, Br) shifts in aromatic (benzene/naphthalene) annealed 1,3-pentadiene system. Notable correlations between various aromaticity index NICS(0,1) with activation barriers show that aromaticity of transition structure in pericyclic reaction can drive the stereochemical course of a reaction. The distinct effect of fluorine to other halogens is the antara migration while the other halogens (Cl & Br) prefer supramode.

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Brown, Paul A., Caleb D. Martin, and Kevin L. Shuford. "Aromaticity of unsaturated BEC4 heterocycles (E = N, P, As, Sb, O, S, Se, Te)." Physical Chemistry Chemical Physics 21, no. 34 (2019): 18458–66. http://dx.doi.org/10.1039/c9cp02387a.

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Acke, Guillaume, Sofie Van Damme, Remco W. A. Havenith, and Patrick Bultinck. "Quantifying the conceptual problems associated with the isotropic NICS through analyses of its underlying density." Physical Chemistry Chemical Physics 21, no. 6 (2019): 3145–53. http://dx.doi.org/10.1039/c8cp07343k.

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Woon, Kai Lin, Azhar Ariffin, Kar Wei Ho, and Show-An Chen. "Effect of conjugation and aromaticity of 3,6 di-substituted carbazoles on triplet energy and the implication of triplet energy in multiple-cyclic aromatic compounds." RSC Advances 8, no. 18 (2018): 9850–57. http://dx.doi.org/10.1039/c8ra00674a.

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Howard, S. T., and T. M. Krygowski. "Benzenoid hydrocarbon aromaticity in terms of charge density descriptors." Canadian Journal of Chemistry 75, no. 9 (1997): 1174–81. http://dx.doi.org/10.1139/v97-141.

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Hartree–Fock/6-31G** calculations on the benzenoid hydrocarbons benzene, naphthalene, phenanthrene, anthracene, pyrene, tetracene, triphenylene, chrysene, perylene, and coronene are used to investigate the link between aromaticity and the electron distribution. Topological charge density analysis is used, concentrating on the electron distribution ρ (and its Hessian) at bond and ring critical points. With regard to the bond critical point data, it is shown that ρc, [Formula: see text]ρc, and the bond "ellipticity" ε are closely correlated with the bond lengths so, as aromaticity indicators, they have little to add over and above existing indices based on structure. However, the same properties evaluated at the ring critical points in the total density, and also at the equivalent stationary points in the π and σ densities, correlate closely with two different aromaticity indices (one based on structure, the other on magnetic properties), the curvature of ρ perpendicular to the ring plane giving (marginally) the best results. Hence a ring critical point (RCP) index is proposed as a way of quantifying aromaticity, based directly on the electron distribution. Keywords: quantum chemistry, electron density, aromaticity, aromaticity index, HOMA, NICS.

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