Chemical shifts resonance

Kidd and Spinney (201) ascribed the fact that only seven chemically shifted resonances are detected for the [NbCl Br6 ] system to the non-statistical formation of the mixed halogenoniobates by concluding that only the cis isomer is formed for those constituents where geometric isomerism is conceivable. This view has recently been challenged (202) and definitive proof is given for the statistical coexistence of all ten possible isomers. The failure to observe the remaining isomers is definitely due to instrumental limitations, i.e. the... 

Detailed examination of chemically shifted resonances can reveal fine structure splitting that is governed by the scalar spin-spin coupling constant (J) that reflects the energetic interaction between magnetically different nuclei. Again J provides information about molecular structures. 

A considerable advantage of 1 3 C nmr spectroscopy is the large range of chemical shifts. Resonance frequencies for most organic molecules are spread over 200 ppm. Additionally, with complete proton decoupling each magnetically non-equivalent carbon appears... 

It is easier to assign a structural model when the synthesized polymer has known structural or compositional features that establish chemical shift resonance-stmcture relationships. 

Two nuclei of the same chemical species, with a J -coupling comparable to the difference between their chemically shifted resonant frequencies are known as AB system and the treatment is a little bit more involved [5, 12]. 

Many Al spectra have now been reported which contain several chemically shifted resonances of a wide range of linewidths, and this also brings problems. The first is that it is not possible to be sure that all the resonances are narrow enough to observe on a given equipment. It is thus always wise to check, at least on some representative samples, that the FID initial intensity has the value to be expected for that concentration of aluminum, by comparison with, for example, an aqueous salt solution of known concentration. A useful aid to this end is an ability to obtain a numerical printout of the numbers in the first few memory locations. A second... 

The required decoupling field can be calculated. Consider a system with chemically shifted resonances that occur in a frequency range of following the method of Lyerla [16]. The effective field in the rotating frame is given by... 

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