The Chemical Shift

Jameson, Cynthia J.; Mason, Joan

doi:10.1007/978-1-4613-1783-8_3

Cited by 70 publications

(48 citation statements)

References 157 publications

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“…Ramsey, 23 Flygare, 24 and Deverell 25 each have demonstrated the connection between paramagnetic shielding and spinrotation constants, and, where both are available, absolute chemical shielding scales, relative to the bare nucleus at 0 ppm, have been determined for several nuclei. 26 No such scale has been reported for cobalt. A plot of the 59 Co chemical shift Vs the spin-rotation constants determined for the three complexes in this study, extrapolated to a spin-rotation constant of zero, provides a value of -3578 ( 1137 ppm relative to 1.0 M K 3 -[Co(CN) 6 ] (aq) for the diamagnetic contribution to the 59 Co chemical shielding.…”

Section: Discussionmentioning

confidence: 95%

Cobalt-59 Nuclear Magnetic Relaxation Studies of Aqueous Octahedral Cobalt(III) Complexes

1996

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Variable-temperature 59 Co nuclear magnetic longitudinal relaxation and line width measurements have been performed on dilute aqueous solutions of 12 octahedral cobalt(III) complexes spanning a large range of isotropic chemical shifts (-1-12 570 ppm) at two fields (4.7 and 11.7 T). A variable-concentration 59 Co longitudinal relaxation study of Na[Co(ethylenediaminetetraacetate)] was performed, and the results of this study indicated a need for the use of dilute solutions. The quadrupolar mechanism of relaxation was found to be dominant for 59 Co nuclei in diamagnetic octahedral complexes in aqueous solution, and values of the quadrupolar coupling constants in all 12 complexes have been determined. At temperatures above 323 K, the spin-rotation relaxation mechanism contributes to the overall rate of relaxation for 59 Co in cobalt(III) complexes with high local symmetry or large moments of inertia. Previous claims that the chemical shielding anisotropy mechanism of relaxation is also a major contributor to the total 59 Co relaxation in cobalt(III) complexes are apparently unjustified. We believe that the previous incorrect conclusions were due to concentration-dependent relaxation behavior that we and others have recently observed. An approximate absolute chemical shielding scale for cobalt is also presented.

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Section: Discussionmentioning

confidence: 95%

Cobalt-59 Nuclear Magnetic Relaxation Studies of Aqueous Octahedral Cobalt(III) Complexes

1996

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“…This effect is strongest for the inner-core shells-1 s in particular. Therefore, it is mostly independent of the chemical environment of the selenium atom [38]. Other relativistic effects are probably not yet important for nSe chemical shifts.…”

Section: International Journal Of Quantum Chemistrymentioning

confidence: 99%

The calculation of NMR shielding tensors based on density functional theory and the frozen-core approximation

Schreckenbach

Ziegler

1996

Int. J. Quantum Chem.

160

136

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rnThe application of the frozen-core approximation to the calculation of the shielding tensor of nuclear magnetic resonance (NMR) spectroscopy is discussed and an implementation is presented. A complete formulation of the shielding calculation within the frozen-core approximation is given, both in general t e r m and for the special case of density functional theory (DFT) and "gauge including atomic orbitals" (GIAOs). The practical implementation is validated by a detailed discussion of the consequences of the approximation. The general conclusion is drawn that the frozen-core approximation is a useful tool for shielding calculations-if the valence space is increased to contain at least the ns, np, ( n -l)p, ( n -l ) d (fourth period and higher) shells, where n is the number of the given period in the periodic table of elements. The new method is applied to nSe shieldings and chemical shifts for a small number of compounds. The agreement between theory and experiment is good for relative shifts, whereas calculated absolute shieldings are generally too small by about 300-400 ppm. This difference is attributed to the relativistic contraction of the core density at the selenium atom that had been explicitly incorporated into the experimental absolute shielding scale. 0 1996 John Wiley & Sons, Inc.of chemistry and beyond. The range of nuclei that can be studied by NMR is steadily increasing. Thus, the area of multinuclear NMR, i.e., the study of nuclei other than--say-',*H, I3C, l4,I5N, I9F, 31 P, or 33S, is rapidly gaining importance [ll.The theoretical prediction of shielding tensors has a long and successful history. These calculations are carefully reviewed annually [21. A good

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“…The deshielding is the greater the lower the excitation energy, the greater the imbalance of charge in the valence shell of the observed atom and the closer the circulation is to the nucleus, that is the higher the electronegativity of the ligands (and if there is a positive charge on the observed atom) 22 . The relatively high energy of n → σ * circulations in hydrazine derivatives (Table 2), in which nitrogen is singly bonded, and pyramidal, correlates with relatively high shielding.…”

Section: Nitrogen Shielding In Azo Azoxy and Hydrazo Compoundsmentioning

confidence: 99%

NMRSpectroscopy of Azo, Azoxy and Hydrazo Compounds

Mason

2009

Patai's Chemistry of Functional Groups

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Introduction: Nitrogen NMR Spectroscopy 15 N and 14 N Techniques Nitrogen Shielding in Azo, Azoxy and Hydrazo Compounds Nitrogen Shielding Tensors Spin–Spin Couplings to Nitrogen in Azo, Azoxy and Hydrazo Compounds

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The Chemical Shift

Cited by 70 publications

References 157 publications

Cobalt-59 Nuclear Magnetic Relaxation Studies of Aqueous Octahedral Cobalt(III) Complexes

Cobalt-59 Nuclear Magnetic Relaxation Studies of Aqueous Octahedral Cobalt(III) Complexes

The calculation of NMR shielding tensors based on density functional theory and the frozen-core approximation

NMRSpectroscopy of Azo, Azoxy and Hydrazo Compounds

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