You need to measure a 13C-NMR for all new compounds, that’s a golden rule. But what do you do when you can’t dissolve more than, say, 5 mg, of your stuff? Either you can’t afford to dump more of it in DMSO, never to be seen again*, or it just isn’t soluble enough.
In that case you simply try anyway, run an overnight experiment on a 400 MHz machine, and hope for the best. Sometimes it will work, sometimes it won’t.
What you always get is the massive solvent signal. On the left, there are some tiny bumps in the background noise, mocking me, that might just be the beginnings of real peaks. Of course there should be many more peaks than the three you can hardly see.
What now? I can hand this over to the NMR service. The first thing they will ask is: “Why don’t you give us a more concentrated sample?” In the past, I even had to redo a synthesis in order to get enough material for a missing carbon spec. Naturally, I should have started the synthesis on a larger scale, but somehow I always end up with those ominous 10 mg of end product. I hate sacrificing so much precious product to the DMSO god!
* I know it is possible to evaporate DMSO, but it takes forever. Also, the material I get out of it is usually an ugly, sticky oil instead of the nice solid I started with.