Examinando por Autor "Ruiz, Lina"

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    Interpreting Aromaticity and Antiaromaticity through Bifurcation Analysis of the Induced Magnetic Field
    (ChemistryOpen, 2019-03) Pino-Rios, Ricardo; Cárdenas-Jirón, Gloria; Ruiz, Lina; Tiznado, William
    In all molecules, a current density is induced when the molecule is subjected to an external magnetic field. In turn, this current density creates a particular magnetic field. In this work, the bifurcation value of the induced magnetic field is analyzed in a representative set of aromatic, non-aromatic and antiaromatic monocycles, as well as a set of polycyclic hydrocarbons. The results show that the bifurcation value of the ring-shaped domain adequately classifies the studied molecules according to their aromatic character. For aromatic and nonaromatic molecules, it is possible to analyze two ring-shaped domains, one diatropic (inside the molecular ring) and one paratropic (outside the molecular ring). Meanwhile, for antiaromatic rings, only a diatropic ring-shaped domain (outside the molecular ring) is possible to analyze, since the paratropic domain (inside the molecular ring) is irreducible with the maximum value (attractor) at the center of the molecular ring. In some of the studied cases, i. e., in heteroatomic species, bifurcation values do not follow aromaticity trends and present some inconsistencies in comparison to ring currents strengths, showing that this approximation provides only a qualitative estimation about (anti)aromaticity.
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    Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives
    (Wiley-VCH Verlag, 2015-06) Torres-Vega, Juan J.; Vásquez-Espinal, Alejandro; Ruiz, Lina; Fernández-Herrera, María A.; Alvarez-Thon, Luis; Merino, Gabriel; Tiznado, William
    The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R2>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)Fn, where n=1-5). © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Which NICS method is most consistent with ring current analysis? Assessment in simple monocycles
    (Royal Society of Chemistry, 2018) Báez-Grez R.; Ruiz, Lina; Pino-Ríos R.; Tiznado W.
    The aromaticity of benzene, Al42- cluster, cyclopropane, borazine and planar cyclooctatetraene (COT) was analyzed according to different strategies based on nucleus-independent chemical shift (NICS) computations. The analysis of NICS-components evolution along the main molecular axis seems to be the most adequate and simplest strategy to predict the aromatic or antiaromatic character of the studied systems. Moreover, the analysis of the σ- and π-electron contributions to the out-of-plane component of NICS (NICSzz) leads to the same qualitative and quantitative conclusions previously obtained by the analysis of the magnetically induced ring current densities. © 2018 The Royal Society of Chemistry.