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Coordination lanthanide-induced shifts

The first applications of lanthanide induced shifts (LIS) in 13C NMR appeared in 1971. (7-10) Shortly thereafter it was shown (11) that Eu(dpm)3 induced chemical shift changes in cholesterol which extended from the coordination site at C-3 clear across the ring system, the assignments used being those of Roberts group. (2) Although the LIS... [Pg.200]

The angular and distance information provided by the lanthanide induced shift has found widespread application from the determination of solution structures of Ln chelates [18,19] to gaining structural information on proteins, nucleotides and amino acids [19], More recently anion binding to coordinatively unsaturated lanthanide complexes has been effectively signalled as the observed lanthanide induced shift has been directly correlated to the nature of the donor atom in the axial position [8,20,21], It is the polarisability of the axial donor that ranks the second order crystal field coefficient, B02, and hence determines the magnitude of the observed shift. Values of the mean shift of the four most-shifted axial protons of the 12-Nq ring for [Yb.la]3+ are collated in Table 2. [Pg.125]

This method of resolution of polyolefins has been extensively studied for cyclooctatetraene systems where excellent enantiomeric excesses are normally observed. Lanthanide-induced shifting can be used to determine the diastereoisomeric composition of the urazoles. Alternate means for the resolution of polyenes based on kinetic resolution using (+)-tetra-2-pinany Iborane have been described, but this reagent consumes valuable substrate. Chiral platinum complexes can also be used but at prohibitive cost on a large scale and with poor regioselec-tivity when several coordination sites are present. [Pg.146]

Shift Reagents. In 1970, Williams, elaborating on the preliminary work of Hinckley, discovered that adding trw-jS-diketonate lanthanide complexes to solutions of substances with lone pairs of electrons available for coordination (such as oxygen- and nitrogen-containing organic compounds) resulted in vastly more dispersed NMR spectra. This phenomenon, named lanthanide-induced shift (LIS), arises from the... [Pg.347]

Chemists did not follow the caution voiced by Weissman [30] that both contact and pseudocontact (dipolar) shifts are to be expected in molecules coordinated to Europium shift reagents. Numerous workers applied a simplified form of the McConnell Robertston relationship (Equation (3)) for pseudocontact interaction as the sole interpreter of the lanthanide induced shifts in rigid organic molecules. It has been shown that especially when C data are compared to H data [31], that both the dipolar and contact effects operate simultaneously ... [Pg.235]

These facts lend significance to lanthanide-induced shift data concerning eusiderin-B (15.2a). Coordination with Pr affects H-7 (A 9.2 ppm) less strongly than H-8 (A 19.2 ppm), and the methoxyl must thus, be located closer to the latter site (as in 15.2a) and not to the former (as in 86a). Structure 15.2a for eusiderin-B was corro-... [Pg.57]

The silver ion coordinates with the soft Lewis base and the lanthanide induces the shifts. Chiral binuclear reagents have been applied to chiral olefins and aromatics. Binuclear reagents formed using the dcm ligand are not effective for chiral resolution, presumably because this ligand is too sterically hindered to permit formation of the tetrakis chelate anion. Experimentation is often needed to find the correct combination of lanthanide and silver P-diketonate to cause enantiomeric resolution. [Pg.419]


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See also in sourсe #XX -- [ Pg.507 , Pg.508 , Pg.509 ]




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Coordination-induced shifts

Induced shifts

Lanthanide shift

Lanthanide-induce shifts

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