Descripción: The set of 1:1 and 2:1 complexes of XOOX′ (X, X′ H, CH 3) with lithium cation has been studied to determine if they are suitable candidates for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. Conventional nuclear magnetic resonance is unable to distinguish between enantiomers in the absence of a chiral solvent. The criterion for experimental detection is valuated by the isotropic part of nuclear shielding polarisability tensors, related to a pseudoscalar of opposite sign for two enantiomers. The study includes calculations at coupled Hartree-Fock and density functional theory schemes for 17O nucleus in each compound. Additional calculations for 1H are also included for some compounds. A huge static homogeneous electric field, perpendicular to the magnetic field of the spectromer, as big as ≈1.7 108 V m -1 should be applied to observe a shift of ≈1 ppm for 17O magnetic shielding in the proposed set of complexes. © 2011 American Institute of Physics.

Descripción: A theoretical study of the relation between the relativistic formulation of the nuclear magnetic shielding and spin-rotation tensors is presented. To this end a theoretical expression of the relativistic spin-rotation tensor is formulated, considering a molecular Hamiltonian of relativistic electrons and non-relativistic nuclei. Molecular rotation effects are introduced considering the terms of the Born-Oppenheimer decomposition, which couple the electrons and nuclei dynamics. The loss of the simple relation linking both spectral parameters in the non-relativistic formulation is further analyzed carrying out a perturbative expansion of relativistic effects by means of the linear response within the elimination of the small component approach. It is concluded that relativistic effects on the spin-rotation tensor are less important than those of the nuclear magnetic shielding tensor. © 2012 American Institute of Physics.

Descripción: In the present work, numerical results of the nuclear spin-rotation (SR) tensor in the series of compounds HX (X=H,F,Cl,Br,I) within relativistic 4-component expressions obtained by Aucar [J. Chem. Phys. 136, 204119 (2012)10.1063/1.4721627] are presented. The SR tensors of both the H and X nuclei are discussed. Calculations were carried out within the relativistic Linear Response formalism at the Random Phase Approximation with the DIRAC program. For the halogen nucleus X, correlation effects on the non-relativistic values are shown to be of similar magnitude and opposite sign to relativistic effects. For the light H nucleus, by means of the linear response within the elimination of the small component approach it is shown that the whole relativistic effect is given by the spin-orbit operator combined with the Fermi contact operator. Comparison of "best estimate" calculated values with experimental results yield differences smaller than 2-3 in all cases. The validity of "Flygares relation" linking the SR tensor and the NMR nuclear magnetic shielding tensor in the present series of compounds is analyzed. © 2013 American Institute of Physics.