QUANTA/NMR

Tetraneopentyl zirconium reacts in the same way as tetraneopentyl titanium to give, on a silica (soo), a tris(neopentyl) monografted species [32]. Treatment under H2 of this surface species yields silica-supported zirconium hydrides [33], which have been characterized as a mixture of mono- (65-70%) and bis- (35-30%) hydrides based on double quanta NMR experiments (Scheme 2.11) [34]. Interestingly, the double quantum experiment allows us to prove not only the presence of the two hydrides and the monohydride of zirconium by the presence or the absence of the double quanta correlation but also to detect the through space magnetic interaction between the zirconium monohydride and the silicon di-hydride, proving thus the spatial arrangement on the surface. This confirms the mechanism by which these hydrides have been formed on the surface. 

Multidimensional homonuclear Double-Quanta Proton-Proton NMR. 2D double-quanta NMR sequences (Scheme 6, sequencespost-C7 or BABA ) allow the selective observation of neighboring protons which interact through dipolar coupling. Therefore, the 2D spectra provide a 2D map with the chemical shift scale in the F2 dimension e.g. 0-13 ppm) and the double quanta scale in FI (double scale, e.g. 0-26 ppm). Thus two protons... 

Fig. 8 Following the reaction by double quanta NMR of an exchangeable phenolic H on an hybrid material. Adapted with permission from the authors. ...

Double-quanta NMR allows the recognition of sites and the monitoring of their reactivity, for example, the exchangeable proton of a phenol functionality of an hybrid material (Fig. 8) which disappears and re-appears upon selective post treatment. The high proton density in this hybrid... 

Finally it is also possible to refine the selection rules of this sequence to observe only correlations between three spins (triple quanta NMR (TQ), Scheme 7). By combining DQ and TQ NMR, it has been possible to determine the structure of the amides and imides deriving from the splitting of N2 on silica supported Ta hydride." ... 

Since u = 2ttv, the same relation is obtained as that found in NMR. The approaches are different one leads to the frequency of the quanta that separates both energy states, and the other to the mechanical precession frequency. However, both frequencies are the same. 

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