HMQC-COSY experiment

Figure 2 Basic four-pulse sequence for the proton detected HMQC-COSY experiment [91...

Figure 13 Proton detected HMQC-COSY experiment [10] using a BIRD [36] pulse cluster...

Figure 6.11 A 3D heteronuclear HMQC-COSY spectrum of a tripepiide. The o),-axis represents N chemical shifts, whereas the (Or and 88, copyright (1988), with permission from Academic Pre.ss, Inc.)...

The pulse sequences for HMQC-COSY and HMQC-NOESY experiments are presented in Fig. 6.10. The 3D HMQC-COSY spectrum of a N labeled tripeptide is shown in Fig. 6.11. Since the coherence transfer involved in this experiment is N([Pg.362]

If 2-D NMR techniques are really useful then 3-D ones must be even more so... shouldn t they A number of 3-D experiments have been devised which are in fact, produced by merging two, 2-D experiments together. The results could never be plotted in true 3-D format since etching them into an A3-sized block of glass would not be practical and viewing them as some sort of holographic projection, would probably not be feasible In essence, 3-D spectra have to be viewed as slices through the block which effectively yield a series of 2-D experiments. It is possible to combine techniques to yield experiments such as the HMQC-COSY and the HSQC-TOCSY. 

A 2D 1H-103Rh HMQC experiment was used to show that both the hydrides are connected to a Rh center that resonates at 925 ppm and is coupled to two 31P-nu-clei. A 1H-1H COSY experiment shows that the two hydrides are coupled. 

All one-bond H- C connectivities were established by a heteronuclear multiple-quantum coherence (HMQC) experiment. Partial structures including a tetraene system, a phenyl group and a diol moiety as shown in Figure 27A were determined by a COSY experiment. 

H and C NMR spectroscopies were systematically used to elucidate the structure of C-glycosylflavonoids the assignment of signals was based upon various experiments, HMBC, HMQC, COSY, etc., as shown in the following examples ... 

Fig. 3.28 (continued) The "C/ H-COSY experiments H-detected HMQC (b), H-detected HSQC (c). 

Due to their higher sensitivity, the H detected C/ H-COSY experiments HMQC (Fig. 3.29b) and HSQC (not shown) are more suitable if only small sample amounts are available. 

For the determination of the sign of coupling constants involving tin, 2D correlation spectra in the form of iH- Sn HETC0R2 -29,136 HMQC O- or HMBC43.265 gj-e employed. Due to the good sensitivity, Sn-Sn COSY experiments can be conducted in a... 

In contrast to homonuclear COSY experiments in 2D heteronuclear correlation experiments the two frequency dimensions are assigned to different nuclei. The term COSY is often used to imply homonuclear correlation and in particular H, IH correlation. Consequently heteronuclear correlation experiments either have a specific name related to the processes involved such as IH HMQC or simply have the words "COSY experiment" appended to the detected nuclei as in IH, l c COSY experiment. 

Three dimensional techniques should only be applied in case of overlap in optimally recorded 2D spectra. The basic principle of these experiments is simply to merge two 2D experiments. The addition of a third frequency domain increases the spectral resolution, and gives additional information. The 3D HMQC-COSY spectrum, for example, consists of a set of 2D H- H COSY maps separated according to the 13C chemical shift along the third frequency dimension. Thus moving across l3C, H and H, H planes makes unequivocal assignments possible [66]. 

Fig. 4. The DEPT-HMQC (Kessler et al. 1989b) spectrum of the aliphatic region of ajmaline (5). The adjustable pulse (see Martin and Crouch 1991) was set p = 180° to afford a spectrum in which the methylene resonances have positive intensity and the methine and methyl resonances are negative. Positive methylene responses are presented as solid black contours negative methine and methyl responses are shown as open contours. Practically, the DEPT-HMQC spectrum shown accomplishes the same task as the recently reported GEM-COSY experiment (Domke et al. 1991) but, in our opinion, is more convenient than the GEM-COSY experiment...

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