51V chemical shifts

Since this stereoelectronic effect is absent in the reactant minimum, it is unlikely that a general, intrinsic correlation between 51V chemical shifts and reactivities could exist when the substituents at vanadium are varied. Accordingly, a sharp increase in the barrier is computed when the second methoxy group is introduced (which must now be trans to the leaving methyl in the transition state), affording different trends for the barriers and the 8(51V) values upon successive methoxy substitution (12a). 

Table II Predicted 51V Chemical Shifts and Ethylene Insertion Barriers for V(=Y)Me3...

V Chemical Shifts and Formation Constants for Selected 2-Methyl-3-Hydroxy 4-Pyrone and 4-Pyridinone Complexes of Vanadate at pH 7.0... 

V Chemical Shifts for Selected Hydroxamate Complexes of Vanadate... 

The identities of the two VL complexes are not known with certainty, but the available evidence suggests the -557 ppm-type products arise from monodentate reaction at the carboxylate group, whereas the -544 ppm products derive from monodentate reaction at the nitrogen functionality. Additional products from amino acids with reactive sidechains, as found in serine or aspartic acid, have not been reported.51V chemical shifts for products formed with histidine are similar to those observed for other amino acids, except that an additional signal (-571 ppm) has been observed [66],... 

V Chemical Shifts of Vanadium Dipeptide Chelates in Aqueous Solution... 

V Chemical Shifts of Selected Aqueous Oxobisperoxovanadate Heteroligand Complexes of VL2X Stoichiometry... 

The 51V chemical shifts of hydroxamidovanadates and their heterocomplexes appear to be useful as diagnostic tools. Table 7.1 gives the chemical shifts of a number of... 

FIGURE 7.2 NMR spectrum showing the large influence of coordination of S-containing heteroligands on 51V chemical shifts compared to similar O coordinated ligands in bis(N,N-dimethylhydroxylamine)(heteroligand)vanadium(V) complexes at pH 8.50. Experimental conditions total vanadate, 5.0 mM total Af.AI-di methyl hydroxylamine, 40 mM total cysteine, 90 mM KC1, 1.0 M pH, 8.5. 

V chemical shifts for aqueous peroxo and hydroxamido divanadium(V) complexes... 

V chemical shifts (ppm) observed for selected heteroligand bisperoxovanadate complexes... 

FIGURE 9.1 The 51V chemical shifts of monoanionic alkoxovanadates are shown as a function of their pKa values. Only a selection from all the alkoxo ligands is identified. The solid lines provide a guide for viewing the data, which was taken from the work of Tracey and coworkers [3]. 

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