Notes

When compared to the previous American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 3 ppm the nitrogen dioxide exposure profile merits an exposure rating of AIHA exposure category 1
However, using the newly adopted TLV of 0 ppm the exposure profile receives an exposure rating of category 4. Further evaluation is recommended to determine the current status of nitrogen dioxide exposures. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: additional text on OELs, methods, results, Can the current density map topology be extracted from the nucleus independent and Members of the QCMM, Alliance Ghent-Brussels, Belgium.and Members of the QCMM, Alliance Ghent-Brussels, Belgium and Theoretical Chemistry, Zernike Institute for Advanced Materials and Stratingh Institute for Chemistry, University of Groningen, 9747 AG Groningen, The Netherlands.Aromatic compounds are characterised by the presence of a ring current when in a magnetic field.

As a consequence, current density maps are used to assess (the degree of) aromaticity of a compound. However, often a more discrete set of so-called Nucleus Independent Chemical Shift (NICS) values is used that is derived from the current density. It is shown here that there is no simple one-to-one relationship that allows reconstructing current density maps from only NICS-values. NICS values should therefore not be used as aromaticity indices without analysis of the ab initio computed current density map.Exploring the ring current of carbon nanotubes by first-principles calculations.Wuhan Center for Magnetic Resonance , Wuhan Institute of Physics and Mathematics Ring current is a fundamental concept to understand the nuclear magnetic resonance (NMR) properties and aromaticity for conjugated systems, such as carbon nanotubes (CNTs). Employing Photoinitiator developed gauge including projector augmented wave (GIPAW) method, we studied the ring currents of CNTs systematically and visualized their distribution.

The ring current patterns are determined by the semiconducting or metallic properties of CNTs. The discrepancy is mainly caused by the axial component of external magnetic fields, whereas the radial component induced ring currents are almost independent of the electronic structures of CNTs, where the intensities of the ring currents are linearly related to the diameters of the CNTs. Although the ring currents induced by the radial component are more intense than those by the axial component, only the latter determines the overall NMR responses and aromaticity of the CNTs as well. Furthermore, the semiconducting CNTs are more aromatic than their metallic counterparts due to the existence of delocalized ring currents on the semiconducting CNTs. These fundamental features are of vital importance for the development of CNT-based nanoelectronics and applications in magnetic fields.Concurrence between current density, nucleus-independent chemical shifts, and aromatic stabilization energy: the case of isomeric [4]- and [5]phenylenes.Computational Quantum Chemistry, Technion - Israel Institute of Technology, The 17 isomers of the [4]- and [5]phenylenes have been studied with three different computational levels of current-density analysis (CDA) and by calculation of the out-of-plane contribution to nucleus-independent chemical shifts (NICS(πzz)).

Current-density maps for these isomeric phenylenes are typically dominated by strong paratropic ring currents in four-membered rings. The relative energies of the isomers, which differ only through the effects of differential strain and aromaticity, were computed at the B3LYP/6-311G* computational level. It was found that the three levels of CDA correlate well among themselves and with NICS(πzz). The latter correlation is improved when the ring sum ΣNICS(πzz) for each isomer is correlated to the ring-current sum ΣJ extracted from CDA. The strain-corrected relative energies of the isomers correlate linearly with ΣNICS(πzz). In particular, the compatibility of different summed quantities with easily computed Hückel-London ring currents suggests a simply calculated measure for dealing with global aromaticity of The equilibrium geometries, total energies, and vibrational frequencies of investigated with density functional theory (DFT) method. Our calculation shows structure, and for other species the C(2v) isomer in which two X atoms are contrapuntal is the most stable structure at the B3LYP/6-311 +G(*) level.

Wiberg bond index (WBI) and negative nucleus-independent chemical shift (NICS) value detailed molecular orbital (MO) analysis further reveals that stable isomers of these species have strongly aromatic character, which strengthens the structural stability and makes them closely connected with the concept of aromaticity.Post relocation of industrial sites for decades: Ascertain sources and human risk assessment of soil polycyclic aromatic hydrocarbons.
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