INVERSE NMR SPECTROSCOPY

C. Albaret, D. Loeillet, P. Auge and P.-L. Fortier, Application of two-dimensional H-31P inverse NMR spectroscopy to the detection of trace amounts of organophosphorus compounds related... 

P inverse NMR spectroscopy to the screening of solutions for the presence of organophosphorus compounds related to the chemical weapons convention, Anal. Chem., 76, 392-398 (2004). 

Selected Biological Aspects. - The catalytic antibody-mediated hydrolysis of the insecticide paraoxon (100) and analogues 101 have been investigated with a view to developing antibodies for use in the treatment of insecticide poisoning. Two-dimensional inverse NMR spectroscopy has been applied to the... 

NMR spectroscopy is always struggling for increased sensitivity and resolution, as well as more efficient use of the instrument time. To this end, numerous improvements of the simple inversion-recovery method have been proposed over the years. An early and unportant modification is the so-called fast mversion recovery... 

Barbate G, Ikura M, Kay L E, Pastor R W and Bax A 1992 Backbone dynamics of calmodulin studied by N relaxation using inverse detected two-dimensional NMR spectroscopy the central helix is flexible S/oefrem/sf/ y 31 5269-78... 

Energy differences between conformations of substituted cyclohexanes can be measured by several physical methods, as can the kinetics of the ring inversion processes. NMR spectroscopy has been especially valuable for both thermodynamic and kinetic studies. In NMR terminology, the transformation of an equatorial substituent to axial and vice versa is called a site exchange process. Depending on the rate of the process, the difference between the chemical shifts of the nucleus at the two sites, and the field strength... 

In S-N compounds containing H bonded directly to nitrogen, inverse detection 2D NMR spectroscopy can be applied to give N... 

It was recently found that j3-PCPY can also be used as a radical initiator to obtain an alternate copolymer of MMA with styrene [35], which was only possible in the presence of Lewis acids [36,37] in the past. The kinetics of the system has been formulated as Rp a[/3-PCPY] a[MMA] (l/a[Styrene] The values of kp /k, and AE were evaluated as 1.43 x 10 L mol -s and 87 kJ/ mol, respectively, for the system. NMR spectroscopy was used to determine the structure composition and stereochemistry of copolymers. Radical copolymerization of AN with styrene [38] by using /3-PCPY as the initiator at 55-65°C also resulted in an alternate copolymer. Rp is a direct function of /3-PCPY and AN, and is inversely related to styrene. 

This unusually high stereoselectivity is due to the high barrier to N-inversion and the presence of the electron-withdrawing phthalimido group. It can be demonstrated that the reaction is under kinetic control when the reaction mixtures described above are allowed to warm to temperatures near or above 0 °C, whereupon a partial or complete inversion of configuration at nitrogen can be seen (by NMR spectroscopy). 

Figure 1.39 Representation of an inversion-recovery 7) experiment. (Reprinted from W. R. Croasmun and R. M. K. Carlson, Two-dimensional NMR spectroscopy applications for chemists and biochemists, copyright 1987, p. 13, with permission, from VCH Publishers Inc., 220 East, 23rd Street, New York 10010-4606.)...

CU4S4] species in which the TADDOL-derived ligand was an unexpected sul-fur-monodentate and not a S/X-bidentate ligand. This hypothesis was confirmed by NOE NMR spectroscopy that suggested a different structure for the Cu complex of the alcohol ligand relative to the methylether and the dimethylamino ligands, which could explain the observed stereochemical inversion. 

The spiro dimer of a-tocopherol (9, see also Fig. 6.4) is formed as mixture of two diastereomers by dimerization of the o-QM 3 in a hetero-Diels-Alder reaction with inverse electron demand. Both isomers are linked by a fluxion process (Fig. 6.22), which was proven by NMR spectroscopy.53 The detailed mechanism of the interconversion, which is catalyzed by acids, was proposed to be either stepwise or concerted.53-55... 

Novel cationic methyl and neutral methyl, chloro Pd11 complexes have been synthesized with various functionalized imidazole ligands. For the first time, structurally characterized examples of this type of Pd complex could be obtained. The chelate ligand is shown to adopt a boat conformation. Inversion of the chelate ring was established by NMR spectroscopy. Depending on electronic and steric features of the ligand, the complexes can act as catalysts in the CO/ethylene as well as the Fleck reaction.186... 

Therefore, X-ray diffraction data provide unambiguous evidence that the structural characteristics of BENA are substantially more similar to those of nitroso acetals (418) (Table 3.26) than to enamines and, consequently, the dynamic process observed by NMR spectroscopy is most likely a slow nitrogen inversion. 

The application of 170 NMR spectroscopy to obtain structural information about polyoxoanions, mainly in nonaqueous solution, had been examined and discussed in detail (99). A very useful finding was that chemical shifts are determined largely by metal-oxygen bond strengths. An inverse correlation exists between the 170 shift and the shortest bond length to a given metal. In aqueous solution the existence of [Mo7024]6 could be confirmed by the use of 170 and "Mo NMR spectroscopy (100-104). Evidence for the existence of the three... 

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