Question

Question: The 1 H NMR spectrum of N,N-dimethylformamide shows three singlets at 2.9, 3.0, and 8.0 ppm. Explain why the two groups are not equivalent to each other, thus giving rise to two NMR signals.

Short answer

Answer

Step-by-step solution

 1H NMR

The number of signals in a PMR spectrum is equal to the number of kinds of protons present in the molecule. The splitting of the NMR signal is caused by spin-spin coupling

Non-equivalent proton in NMR

The structure for N,N-dimethylformamide places the two CH₃ groups in different environments and different chemical shifts. One CH₃ group is cis to the O atom, and one is cis to the H atom.

This gives rise to two different absorptions for the CH₃ groups.

Representation of cis

It should be noted that spin-spin splitting is observed only between non-equivalent neighboring protons.