ROESY correlation

In order to combat this, the rotating frame Overhauser effect spectroscopy (ROESY) techniques can be employed. An in-depth discussion of how this technique works is outside the remit of this book but suffice to say, in the ROESY methods (1- and 2-D), NOE data is acquired as if in a weak r.f. field rather than in a large, static magnetic field and this assures that all NOEs are present and positive, irrespective of tumbling rate and magnet size. It is possible that some TOCSY correlations can break through in ROESY spectra but these will have opposite phase to the genuine ROESY correlations and so should therefore not be a problem - unless they should overlap accidentally with them. A 2-D ROESY spectrum of the naphthalene compound is shown below (Spectrum 8.6). 

We end our discussion of VGSE by comparing the ROESY correlations of the amide protons with the corresponding interactions in COSY and TOCSY. Figure 5.35 shows comparable sections of each spectrum. We have the seen the COSY and TOCSY portions earlier and showed how these spectra, along with the HMQC, can be used for intra-residue assignments. The ROESY correlations, on the other hand,... 

Critical data (a) HMBC correlation (H2-8/C-6) =the Jch cross peakof CD3OD, (b) the ROESY correlation (OH/ H-19) was very weak, (c) the revised structure was supported by DFT calculations and X-ray structure. 

Owing to these data, three possible skeletons were proposed head to tail (75) or head to head (20 and 76) (Scheme 8). It is worth noting that the theoretically other symmetrical combinations of these two 14,15-dihydrovirosecurinine units around the cyclobutane ring are not compatible with the observed ROESY correlations, even if not discussed by the authors. 

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