Spin saturation transfer study

Spin saturation transfer studies of the 31p NMR of the iso-propyl complex yield data regarding the rate of interconversion of the dihydride and molecular hydrogen complexes. Thus ki is calculated to be 63 s-1 (299 K) and k-i is calculated to be 12.4 s-l(300 K). These values are in reasonable agreement with the corresponding values determine by stopped-flow kinetics for the cyclohexyl complex as described above ki = 37 S l(298 K) and k-i = 18 S l (298 K). Activation parameters for conversion of the dihydrogen to dihydride reaction (kq step) were determined based on analysis of the spectral changes in the temperature range 288-310 K. The values Zij = 16.0 0.2 kcal/mole, AI = 10.1 1.8 kcal/mole and -19.9 6.0 cal/mole deg were determined. 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

These experiments while moving beyond simple structure determination, still depend primarily on structure determination as their primary tool. A number of experiments have moved beyond this to exploit other characteristics of NMR. For example, spin saturation transfer can be used to study internal rotation of molecules (59, 60), and line shape analyses can be used to study intramolecular exchange processes (61), conformational interchange (62) and... 

Alkylaryl ethers and diaryl ethers undergo protonation on either oxygen or carbon, depending upon the acidity of the medium87 (Scheme 4.3). Both the C-protonated species 28 and the (9-protonated species 29 have been observed. The evidence mainly comes from NMR and UV data. Sommer et al.88 have used para-anisaldehyde as an indicator in acidity measurements in the superacidity range. The barrier of rotation around the Cipso—0 bond upon (9-protonation has been used as a criterion in such studies. The torsional barrier around the phenyl-alkoxy bond in the C-protonated forms of aromatic ethers has also been measured by spin-saturation transfer measurements.89... 

Fluxionality studies have been carried out on 343 (Scheme 44).137 No coalescence of the two allene hydrogens (HI and H6) was observed in temperature ranges where the complex is stable (ca. 100°C). However, spin saturation transfer was observed between 60 and 100°C, which yielded activation parameters (AH = 26.8 1.3 kcal/mol A5J = 15.1 1.3 eu) for migration of the metal between the two double bonds. At 80°C, 343... 

The methods available to determine reaction rates by NMR spectroscopy include line broadening, spin saturation transfer and exchange spectroscopy (EXSY). The latter approach can be completed by both 1 and 2 D procedures. Several studies in the literature have served to illustrate that the dynamic behaviom of complexes detected through the parahydrogen effect can be examined. A general feature of this approach has involved the refocusing of the initial antiphase magnetisation. 

PARAMETERS DETERMINED BY IH NMR STUDIES OF DIHYDROGEN-DIHYDRIDE EQUILIBRIUM (Kequil= 0.2-OJ) AND SPIN-SATURATION TRANSFER... 

This mechanism, however, turned out abortive because still earlier it was firmly -established, by the method of spin saturation transfer (cf. Ref. that the nitro group in this ion, if not exclusively, then at iKist mostly, migrates to the neighbouring positions by a 1,2-shift. Similar results have been obtained in studying the mechanism of the shifts for the other migrants in ions of this type CH3... 

---