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Nucleus-independent chemical shifts (NICS) have been used extensively for the identification of aromaticity properties of molecules, ions, intermediates, and transition states since their introduction in 1996 by Schleyer et al. Initially, probes (bq's) were placed at the centers of systems (NICS(0)) and later, 1A above the molecular planes (NICS(1)).(More)
[structure: see text] The parent and dipropyl-substituted anti (1a,b) and syn doublebent (2a,b) [5]phenylenes have been assembled by CpCo-catalyzed double cyclization of regiospecifically constructed appropriate hexaynes. (1)H NMR, NICS, and an X-ray structural analysis of 1a reflect the aromatizing effect of double angular fusion on the central ring of the(More)
Localized benzene derivatives can be separated into two classes, one that retains large diamagnetic ring currents and a second that loses the diamagnetic ring current. Energetic criteria and NICS scan are used to evaluate the nature of the two classes. Hückel-type treatment, MO analysis, and comparison to model compounds suggest that there is no connection(More)
This review describes the current state of magnetic criteria of aromaticity. The introduction contains the fundamentals of ring currents in aromatic and antiaromatic systems, followed by a brief description of experimental and computational tools: NMR, diamagnetic susceptibility exaltation, current density analyses (CDA) and nucleus independent chemical(More)
[reaction: see text] The total synthesis of C(3)(h)-symmetric [7]phenylene has been accomplished by triple cobalt-catalyzed cycloisomerization of an appropriate nonayne. Its spectral data are in accord with the expectations for a triply angularly fused system, but its calculated heat of formation suggests the presence of a destabilizing sigma effect(More)
Nucleus-independent chemical shift (NICS)-based methods are very popular for the determination of the induced magnetic field under an external magnetic field. These methods are used mostly (but not only) for the determination of the aromaticity and antiaromaticity of molecules and ions, both qualitatively and quantitatively. The ghost atom that serves as(More)
A symmetrical tetraazaacene incorporating a central cyclobutadiene ring was calculated in different oxidation (hydrogenation) states, displaying different tautomers and conformers. Geometries, thermodynamics, and electronic properties were computed, and the aromaticity of all these species was calculated on a per ring basis by NICS-scans and NICS-X-scans.(More)