2D NMR method

More generally, note that the applieation of almost any multiple pulse sequenee, where at least two pulses are separated by a time eomparable to the reeiproeal of the eoupling eonstants present, will lead to exehanges of intensity between multiplets. These exehanges are the physieal method by whieh eoupled spins are eorrelated in 2D NMR methods sueh as eorrelation speetroseopy (COSY) [21]. 

Orrell K G, Sik V and Stephenson D 1990 Quantitative investigations of moieouiar stereodynamios by ID and 2D NMR methods Prog. Nucl. Magn. Reson. Specfrosc. 22 141-208... 

A second 2D NMR method called HETCOR (heteronuclear chemical shift correlation) is a type of COSY in which the two frequency axes are the chemical shifts for different nuclei usually H and With HETCOR it is possible to relate a peak m a C spectrum to the H signal of the protons attached to that carbon As we did with COSY we 11 use 2 hexanone to illustrate the technique... 

Fattorusso s group, which earlier had discovered 48-50 in Axinella cannabina, reported the occurrence of another spiroaxane series, 51 and 52, from Acanthella acuta. The habitat of the latter sponge is the Bay of Naples. As was the case with other metabolites reported in their recent studies, the investigators deduced the structures of isonitrile 51 and iso thiocyanate 52 chiefly by 2D NMR methods. 

D-NMR methods are highly useful for structure elucidation. Jeener described the principles of the first 2D-NMR experiment in 1971 [31]. In standard NMR nomenclature, a data set is referred to by one, i.e., less than the total number of actual dimensions, since the intensity dimension is implied. The 2D-data matrix therefore can be described as a plot containing two frequency dimensions. The inherent third dimension is the intensity of the correlations within the data matrix. This is the case in ID NMR data as well. The implied second dimension actually reflects the intensity of the peaks of a certain resonance... 

This ladybird is protected by hyperaspine (23) (Fig. 4), the structure of which was deduced from its ID and 2D NMR data. These spectra disclosed the presence in the molecule of a 3-oxaquinolizidine skeleton substituted by a 2-pyrro-lecarboxylate moiety, by a secondary methyl group, and by a n-pentyl side chain. The ds-fused ring conformation and the relative configuration of 23 were based on IR and 2D NMR methods [37]. 

Contemporary approaches to chemical stmcture elucidation are now heavily reliant on mass spectrometry and NMR spectroscopy. Since the advent of 2D NMR methods, in many laboratories vibrational data are either not acquired or not considered, which represents a paradigm shift from approaches to chemical structure elucidation as recently as 20 years ago when vibrational spectroscopic data were an integral part of the structure elucidation data assembled to characterize an unknown structure. In contrast, we have found it useful to continue to acquire and utilize vibrational data for the characterization of impurities and degradation products [64,65]. 

Fig. 6.11 Three isomers of Ca)H36 produced via transfer hydrogenation and identified using 2D NMR methods Schlegel diagrams (a-c) and representative space filling model (d) (a) Cx isomer, (b) a C3 isomer and (c) a T isomer (Gakh et al. 2003) (Reprinted with permission from the American Chemical Society)...

Multidimensional NMR spectroscopy proves to be a powerful method to reveal structural and dynamical information at the molecular level in elastomers. Residual dipolar couplings can be measured site-selectively and correlated with the crosslink density and mechanical stress. The local segmental order and information on local molecular motions can be also obtained with newly developed 2D NMR methods. The information at the molecular level can be correlated with macroscopic properties of elastomers and provides the basis for a better design of material properties for specific applications. 

Next, Schmitz and colleagues116 reported the isolation and characterization of malayenolides AD, series of novel diterpenes from the Indonesian sea pen Veretillum malayense. The structures were elucidated using proton-detected 2D-NMR methods in conjunction with the use of 3 mm NMR probe technology. The structure of malayenolide-A (53) is shown. 

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