THE NMR SPECTRA OF OTHER NUCLEI

Although the proton is the most extensively studied nucleus, NMR spectra of other nuclei have been investigated. 

A small number of reports have appeared of the NMR spectra of other low-7 nuclei. These include Cr NMR which has been used in a study of the ferromagnetic materials CdCr2S4 and CuCr2Se4. Information about the magnetic hyperfine interactions in these compounds was derived from the echo formed by multiple quantum effects (Abelyashev etal. 1988). 

NMR spectra of other nuclei have been reported. A problem with NMR is the broadness of the signal because of the adjacent nitrogen atom isothiazole absorbs at -1-53.7 ppm (reference (NH4)2S04) <84CJC98I >. The saccharinate anion has been examined by O NMR the chemical shifts for 0-1 (155 ppm) and 0-3 (275 ppm) (reference H2O) are consistent with extensive contribution from resonance forms such as whereas the sulfur oxygens show little evidence for... 

Apparent NMR equivalence of nuclei can also arise by a quantum mechanical intramolecular tunneling process. In principle, this process may be differentiated from intermolecular exchange processes because although the exchanging nuclei are rendered equivalent insofar as the NMR experiment is concerned, spin-spin splitting by other magnetic nuclei is not washed out. This type of intramolecular exchange is manifested in several boron hydride derivatives. It was first proposed by Ogg and Ray (98) to explain the NMR spectra of aluminum borohydride, whose structure is... 

The MQMAS has now become the most widespread method for the acquisition of high-resolution solid-state NMR spectra of quadmpolar nuclei. The MQMAS step has been incorporated into the other pulse sequences focusing on achieving the correlation between the quadmpolar and spin-1/2 nuclei (i.e., HETCOR-MQMAS). ... 

NMR spectroscopy has assumed a major role in our attempts to understand the structures and functions of molecules. For example, NMR has developed to the stage where it is possible to determine the three-dimensional structures of protein molecules containing thousands of atoms. One reason that this feat is possible is because other nuclei such as l3C and 31P have spin states that respond to an external magnetic field much the same way as does H. Therefore, NMR spectra of these nuclei can also be obtained, thus providing more structural information. The use of NMR to study protein struc-... 

Other nuclei besides H or have been used to monitor enantiomeric discrimination with chiral lanthanide chelates. This includes the NMR spectra of chiral 2-thiabicyclo[4.3.0]nonane 2,2-dioxides (14) and 8,8-dioxides (15) with Pr(hfc)3 . The Si NMR spectrum of a-C-silylated amines and alcohols (38) in the presence of Eu(tfc)3 was used to monitor the optical purity of these compounds . A refocused-decoupled INEPT (insensitive nuclei enhanced by polarization transfer) pulse sequence was used to circumvent the long spin-lattice relaxation times of the silicon. 

For an accurate quantification of the content of substructures, it is essential that the NMR spectra are recorded under appropriate experimental conditions. In general, two effects can falsify the signal intensities (i) an incomplete spin-lattice (Ti) relaxation and (ii) a heteronuclear Overhauser effect, resulting from H decoupling. Typically, the NMR signal quantification is less crucial from the proton spectrum than from spectra of other nuclei, which require the correct choice of experimental conditions. To date, very few relaxation studies have been reported comparing data for terminal, linear, and dendritic units. Longer Tm values were... 

Analysis of the nmr spectra of a large number of known compounds has enabled extensive tables of the 8 values of H, C and other nuclei in a wide variety of structural circumstances to be prepared. 

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