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Logic Puzzle #28: Interference from the Solvent … Solution

With deuterated chloroform, the signals from the solvent can overlap with the signals from the unknown of interest. The following spectra are some examples one may encounter.

In the expanded regions for each 13C NMR spectrum, Cases 1, 2, 3, 4 and 5 display a weak signal at ~76.8, 77.3, 77.5, 77.5, 77.5 ppm, respectively. The weak signals, indicated by blue arrows, are attributed to the unknown of interest.

In all five 13C NMR spectra, a clear, intense triplet is evident. The triplet, labeled with green arrows in Case 1, is a result of the solvent CDCl3. At ~77.2 ppm, a small signal is evident. This signal, labeled with a red arrow, is a result of the solvent CHCl3.