We have a case where we have a molecule has to 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.

We have a case where we have of a molecule that has to 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.

We have a case of a molecule that has to 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.