1,721,023 research outputs found
Critique of the multipath model for 1J(C,C) nuclear spin-spin coupling via electron current induced by 13C nuclear magnetic dipoles
No full textMaps of ab initio electronic current density induced by the permanent magnetic dipole moment of 13C are reported for three saturated hydrocarbons: ethane, cyclopropane, and bicyclobutane. The plots are interpreted via the Biot-Savart law of classical electromagnetic theory by analysing the effects of the magnetic field induced by the current distribution at the site of spin-coupled carbon nuclei. It is shown that, within the proposed model, the significant variation in magnitude and sign of 1J(C,C) characterising these three molecules can be related to different topologleal features of the current density vector field. The general pattern can be rationalised in terms of orbital hybridisation of the coupled carbon atoms: 1J(C,C) does not appear to be significantly affected by the multipath coupling processes usually suggested in the literature. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA
Interpretation of vicinal spin-spin coupling constants in ethane via the current-density induced by nuclear magnetic dipoles
No full textThe indirect nuclear spin-spin coupling is rationalized via electronic current densities induced by nuclear magnetic dipoles. The coupling-density tensor, a function in real space obtained from the current density, visualizes fundamental aspects of the coupling mechanism. Magnetic group theory and current-density plots are used for discussing the Dirac-van Vleck vector model in the contact interaction. The Biot-Savart law is useful for understanding the sign of the contributions to the magnetic field at a nucleus from a given point of the current field. These tools are used to analyze the vicinal spin-spin coupling in ethane. © 2005 Elsevier B.V. All rights reserved
Nuclear spin-spin coupling density functions and the Fermi hole
No full textFermi hole density functions were computed for the first-row hydrides. The relative maps were compared with those of one- and two-bonds nuclear spin-spin coupling density. The plots of density functions demonstrated that the Fermi hole, causing same-spin electron repulsion, drives the fundamental electron-coupled mechanism
Invariance of magnetic-field induced current density to a continuous transformation of the origin of the coordinate system
No full textThe quantum mechanical current density induced by a magnetic field in the electrons of a molecule evaluated via theoretical schemes based on 'continuous transformation of the origin of the current density' (CTOCD), is independent of the origin of the coordinate system, irrespective of other approximations retained in the calculation. Nuclear magnetic shieldings determined by continuous transformation of the origin of the current density are intrinsically origin independent. These statements are also proven for damped CTOCD schemes. Integral conditions for charge-current conservation, equivalent to those for gauge invariance, are satisfied exactly within CTOCD methods for symmetry reasons, e.g., for centrosymmetric molecules. © 2006 Elsevier B.V. All rights reserved
Invariance of magnetic-field induced current density to a continuous transformation of the origin of the coordinate system
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Parity-violating contributions to nuclear magnetic shielding
No full textThe expressions for both diamagnetic and paramagnetic contributions to the nuclear shielding tensor were reported. Even though both contributions depend on the gauge choice, their sum was gauge independent for sufficiently large basis sets. This formalism was implemented within the framework of ab initio response theory and numerical estimates were reported for two molecules
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