Compounds, chemical, formation shielded

Formation of the adduct with dirhodium complex [6] has significantly changed the chemical shift of the compounds in which proton transfer occurred, for example, for the adduct of iV-(5-nitrosalicylidene)-2-ami nobutane, the chemical shift was —198.2, which was shielded by of 110 ppm in comparison to that in the starting Schiff base.12 The large signal shift was due to the shift of the proton transfer equilibrium towards NH tautomer. For the adduct of N-(salicylidene)-2-aminobutane, existing in the OH-form, the 15N chemical shift has changed from —87.5 to — 84.6 ppm. 

NMR techniques as a detailed knowledge of all the NMR parameters, such as chemical shielding anisotropy and quadrupole tensor parameters, as well as their distributions, is necessary to draw detailed conclusions on the local environment and long-range order of V atoms. However, the SATRAS analysis of V MAS spectra coupled with the results of V 3Q-MAS and 5Q-MAS studies (Figure 5.15) can provide this information and demonstrate the formation of a V—P—Ti compound, in contrast to previous hypotheses for such systems. 

One of the most important pieces of progress in recent years is the establishment of a method for the determination of the conformation of the inclusion complex in solution. The method, which takes advantage of the change of the H-chemical shifts of cyclodextrin on complex formation with the aromatic guest compound (mostly due to the anisotropic shielding effect of the aromatic ring of the guest), is briefly described as follows [7-9]. 

Fig. 4. Plot of the changes of the C-chemical shifts in ppm) of the guest compounds on inclusion complex formation with a-cyclodextiin vs. the penetration depth (Z in A) the positive sign in 4 c shows an increase in shielding, and a positive sign in Z shows deeper penetration with respect to the plane ( Z = 0) comprised of the 6 H-3 atoms of a-cyclodextrin the numbering systems of the carbon atoms of the guest compounds are as follows ...

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