May 11, 2009
Yes, it is possible to elucidate an unknown with just a 1H NMR spectrum but only for specific cases*. Case 1: an unknown with a low molecular weight and a “well-resolved” 1H NMR spectrum. Case 2: the unknown has been identified previously, or at least part of it, in a database/library/literature and a spectrum search produced a hit(s).
*Please note that as I write this blog, only two cases come to mind perhaps there are more. If anyone can think of more cases, please feel free to comment so I may expand this blog.
Elucidations based solely on a 1H NMR spectrum can fail when:
-peaks are poorly resolved or crowding each other,
-the 1H NMR spectrum exhibits low signal-to-noise,
-the peaks for the unknown are not clearly distinguished from impurities or artifacts,
-the 1H NMR spectrum is too complicated,
-the unknown contains few characteristic proton signals and/or numerous heteroatoms.