Line contact shift

Let us assume that shifted resonances can be easily followed in a titration of Ln(III), or a Ln(III) complex, with an organic molecule. Let us also assume that we can prove that only a single complex of 1 1 stoichieometry is formed. We can now analyse the shifts on proton, phosphorus or carbon resonance lines by making the reasonable assumption that there is no free electron contact shift except on coordinated atoms. The shifts are then dipolar. Contact shifts will be considered again later. 

A sizeable complex formation shift contribution is noted for aromatic adducts. Sizeable complex formation shifts are also observed (394) for the diamagnetic LSR La(dpm)3. The shifts induced by paramagnetic complexes such as Eu(dpm)3 and Pr(dpm)3 are accordingly corrected for this factor. In this work it is found that contact contributions to the shifts are generally larger in amines than in alcohols or ketones. For quantitative structural work Yb(dpm)3 is found to be particularly useful since it produces minimal contact shifts without any adverse line-broadening. 

Here fVup is the difference in the widths between the broadened and final lines, and /p are the proportions of the reactants present in the diamagnetic and paramagnetic states, respectively, and Sv is the contact shift. 

The paramagnetic behavior of nickel Schiff bases is attributed to the diamagnetic, square planar-paramagnetic octahedral equilibrium shown in Figure 3.9. The contact shifts for nickel(II) Schiff bases are generally very large (e.g., —35 to +70 ppm) and result in simple first-order spectra with one line for each chemically distinct set of nuclei. 

Lanthanide induced chemical shifts have been studied.280 l,2-Dithiole-3-thiones did not give any contact shifts with Eu(fod)3 and Pr(fod)3, whereas l,2-dithiol-3-ones gave moderate shifts. Attempts to define the position of lanthanide complexing were made for the l,2-dithiol-3-ones it was not possible to define the position of the lanthanide atom closer than 2-3 A from the oxygen and 40-50 on either side of the C—O line. 

In the absence of gravity a spherical particle of radius r will be oriented in such a way that the energy of the system is minimized. This means that the change (first variation) in the interfacial free energy when the contact line is shifted by a small distance, 5h, is zero. It follows from geometry that a shift in the position of the contact line by 5 h downward from its initial position (bold line in Fig. HI-20) results in changes in the interfacial areas of the solid-gas (SSG), solid-liquid (SSL), and liquid-gas (SLB) interfaces equal to... 

To obtain electron-spin densities it is necessary to distinguish Fermi contact shifts from the pseudocontact shifts for each compound. This may be done sometimes by comparing two series of complexes differing only in central metal ion, if it can be shown that the modes of spin delocalisation are identical but one member is magnetically isotropic. Alternatively, the shifts for a given nucleus in the paramagnetic species are compared in solution and in the solid. Fermi contact shifts are the same in fixed and mobile phases the ratio of pseudocontact shifts in fixed and mobile environments is related to the g-value anisotropies. (While theoretically generally applicable the method is restricted because of the wide lines obtained with solids.) Discrimination between... 

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