June 15, 2009
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs
One of the trickiest parts of interpreting NMR data is identifying what signal belongs to the unknown compound and what can be classified as an impurity. In this case, impurities are described as extra signals coming from a solvent(s), a side product(s), extraction/purification process, etc.
The 1H NMR spectrum below is for an unknown compound. The spectrum shows a highly coupled system with the exception of two singlets at 2.14 and 1.68 ppm. In addition, the integrals of the 2 singlets show a relative integral of 1 proton. This indicates the possibility of 2 CH groups adjacent to 3 quaternary carbons. Although is not necessarily incorrect, it does raise 2 yellow flags that either singlet (or both) does not belong to the unknown. The next step would be to check this possibility against 2D NMR data.