0
|
We have a case of a molecule that has two slowly exchanging conformations. In the NOESY experiment we see cross-relaxing cross-peaks (negative or the opposite sign to the diagonal) for interproton distances as well as exchanging cross-peaks (positive or the same sign as the diagonal). This is the classical expected behavior in such a sample. But... In this molecule there is a pair of geminal protons for which the phenomenon is exactly reversed: The interproton cross-peak is POSITIVE and the exchange peaks are NEGATIVE. There is no doubt which peak is which (from the COSY, for instance). I suspect a scrambling effect due to the combined mechanisms, but I hope to be reassured by a clear explanation or comments saying that this has been seen and described before. |
|
0
|
Hi foxx, A recent article by Kuprov et al may provide some hints (I can't say that this is the issue in your case, but this is probably worth a look): http://onlinelibrary.wiley.com/doi/10.1002/anie.201410271/pdf Anomalous Nuclear Overhauser Effects in Carbon-Substituted Aziridines: Scalar Cross-Relaxation of the First Kind. Ilya Kuprov, David M. Hodgson, Johannes Kloesges, Christopher I. Pearson, Barbara Odell, and Timothy D. W. Claridge, Angew. Chem. Int. Ed. 2015, 54, 3697-3701. Pete |
