The appearance of an NMR spectrum is altered if nuclei can change between differ

Question

The appearance of an NMR spectrum is altered if nuclei can change between different environments rapidly.

The N=O group of the below molecule (N,N dimethyl nitrosamine) rotates and as a consequence the magnetic environments of the CH3 groups are interchanged.

On an old 1H-NMR 60MHz instrument, the two CH3 resonances appear as two lines separated by 25Hz. On a1H-NMR 500MHz spectrometer, a single line is observed. What would you deduce from the observation of a single line in the 1H-NMR 500MHz spectrometer? (Write your answer with up to 4 lines of text).

Explanation / Answer

In the NMR spectroscopy, the rotation in the molecular structure changes the chemical shift and the splitting pattern of the protons apprearing in the spectrum. thus in the given molecule, the methyl protons appears as a double, as it couples with the adjacent protons on a 60 MHz instrument. But the same methyl appears as a singlet in the 500MHz instrument as the proton has now been bonded to the oxygen of the N=O linkage due to rotation.

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