I was hoping to use 1D NOESY with an extremely long mixing time to excite protons on the analyte of interest in a mixture and ignore typical distance information desired from NOESY. The molecule I am investigating has many heteroatoms and quaternary carbons, thus TOCSY is not an option. Our resident NMR expert informed me that I should be able to set a much longer than normal mixing time (1 second+) in order to indiscriminately excite everything on the molecule while silencing peaks from other components in the mixture. I think I may have misunderstood him or improperly articulated my question, because a 1D NOESY with a 1 second mixing time targeting the peak unique to my product yields no other peaks. Is there a maximum distance to cause NOESY excitation no matter how long you set your mixing time? Also how long can you make the mixing time before you run the risk of damaging the probe? Unfortunately I don't think that DOSY would be an option for this purpose as two of the components are simple E/Z isomers and would likely diffuse at the same rate.

Can the NOESY mixing time be set to an extremely long duration in order to excite the whole molecule and not just protons within 5 angstroms? Or is this not possible? Is there another experiment I could run for this purpose besides NOESY, DOSY, or TOCSY if not? Separation is proving very difficult and selective excitation of the mixture in NMR would make things much easier.

The attached file is the reaction in question and the peak I wish to target is the methyl group on the sulfur in the product. The isolated spin system precludes the use of TOCSY as far as I understand it. I would have thought that it is close enough to the ethyl group on the nitrogen to at least see peaks from that but I'm not even seeing those. The E and Z versions of the peak are also able to be resolved but again, nothing is being excited by targeting either peak or even both at once.