EXSY spectrum

Figure 6.7 The 3D EXSY-EXSY spectrum of heptamethylbenzenonium sulfate in H.2SO4 representing o i = o)j reflection symmetry. Cross-peaks lying on identical planes (coi, a s) are connected by lines. (Reprinted from J. Mag. Reson. 84, C. Griesinger, et al, 14, copyright (1989), with permission from Academic Press, Inc.)...

Although the kinetics of imidazole exchange between NP2 and its low-spin imidazole adduct are very slow and no chemical exchange cross peaks in the NOESY/EXSY spectrum of a mixture of the high-spin and low-spin forms of NP2 are observed, the V-methylimidazole complex... 

Figure 1.30 EXSY spectrum (CD2CI2, 176 K) showing cross-peaks for the intra- and inter-molecular exchange between nuclei of the monomeric, 107, and dimeric, 108, fo rms of [Rh(dppb)2](BPh4).

Figure 1.32 EXSY spectrum of 112 in CD2CI2 at 240 K, showing pairwise exchange of C nuclei (circled).

Figure 1.33 Possible exchange pathways for the inversion at le in complexes of the type [PtIMejL-L], (L-L = MeTe(CH2)3TeMe and PhTe(CH2)3TePh). je EXSY spectrum of [PtlMe3 Mele(CH2)3leMe ] in CDCI3 at 313 K. The circles indicate the position of the exchange cross peaks between the DL and the meso isomers. No exchange between the two meso isomers is observed in this compound.

Fig. 9. 600 MHz EXSY spectrum showing the exchange of magnetization between ammonium protons and two distinct water components in a peptidyl-water cluster bound to -aminomethyl polystyrene resin swollen in DMF-d1. Reproduced with permission from Ref. 88. Copyright 2001 American Chemical Society.

Modern NMR techniques such as quantitative analysis of multisite exchange using either ID magnetization transfer experiments (JOS) or the 2D exchange spectroscopy (EXSY) method (104,105) promise to be of great help in unraveling the complex stereochemical exchange networks involved in cluster fluxionality. The usefulness of EXSY in the context of this article is illustrated by the phase-sensitive 13C 1H EXSY spectrum (255 K, tm = 0.5 sec)... 

Fig. 4. 13C H EXSY spectrum of [Os3Pt(jt-H)3(CO),Q(PCy3)]+ (21) in the carbonyl region.

Fig. 8.5. 500 MHz EXSY spectrum of Pr(DTPA)2- recorded with the pulse sequence of Fig. 8.2A [4], The spectrum demonstrates the presence of an equilibrium between two conformational isomers.

Fig. 8.6.600 MHz EXSY spectrum of the intermediate reduction product of the 2Fe4S4 ferredoxin from C. pasteurianum. Most signals of the intermediate species display cross peaks from both the fully reduced and the fully oxidized species. The sequence used is that in Fig. 8.2A. tm = 5 ms. A pattern belonging to a single signal exchanging among the three species ((a) fully reduced (b) half reduced (c) fully oxidized) is highlighted as an example.

In the presence of excess diisopropylzinc, the EXSY spectrum in both thf and toluene shows rapid interconversion between zinc-bound isopropyl groups of the zinc reagent and alkoxide dimer (Fig. 15). The reaction occurs for both racemic and homochiral dimers with comparable facility. In toluene, the rate... 

Fig. 15 EXSY spectrum of a mixture of homochiral Zn alkoxide and excess diisopropylzinc in toluene-dg. The exchange peaks at 1-1.5 ppm are Zn-bound methyl groups the high field cross-peak belongs to the isopropyl methine protons...

Figure 7. The 13C EXSY spectrum of the V-HIDA 2 complex formed in 100 mM vanadate and 300 mM HID A at pH 5.13 and 318 K. The carbons assigned to the complex are labeled Cx and those of the ligand as Lx.

A second example is illustrated by the V-Tricine system (25). Its EXSY spectrum, revealing intramolecular exchange, is shown in Figure 10. The V-Tricine complex differs from the V-TEA complex in that the two-pendent hydroxymethyl arms are inequivalent (an ABC system) (46). The rate constants determined for the coordinated arm exchanging with each pendent arm [fc(C4b - C5f) and fc(C4b - C6f)] are very similar (25). Assuming the chemical event is the formation of a single species from which the two pendent arms and the chelated arm is derived, each rate represents only one-third of the exchange rate as shown in equation 6 ... 

Figure 11 shows the contour plots of the 2D 51V EXSY spectrum of a two-site system (40 mM total vanadate at pH 10.9) in which V exchanges with V2. Quantification of the EXSY spectrum and calculation of the error propagated to the rate constants from the integration precision gives a 25% error on the rate constant. The results (both the rate constants and the errors) correspond nicely to the results obtained from a ID magnetization transfer experiment on the same sample (27). The EXSY spectrum of a sample containing 12.5 mM total vanadate at 1.0... 

Figure 22 EXSY spectrum showing stereospecific exchange correlations between bridging and terminal carbonyls in [Rli6(CO)i5 P(4-(MeO)C6H4)3 ], inCDClj at 274 K = 0.02 s...

Figure 6-32 The H EXSY spectrum for the heptamethylbenzenium ion. (Reproduced with permission from R. H. Meier and R. R. Ernst, J. Am. Chem. Soc., 101, 6441 [1979]. Copyright 1979 American Chemical Society.)...

Fig. 16. NMR 2D-EXSY spectrum of an acidic aqueous solution containing the thallium species Tl(OH2)g, TKCN), and T1(CN)2, showing the dominating cyanide...

Figure 8.44. The 128 MHz boron-11 2D EXSY spectrum of a 1 1 mix of BCI3 and BBr3 at 400 K. The spectrum was recorded with a mixing time of 50 ms (reproduced with permission from [51].

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