Why is the activation energy required to rotate the C-N bond in tertiary amides (i.e. N,N-dimethylacetamide) higher than for a primary amide (i.e. acetamide)?

1 Answer
Dr. Hayek
Sep 28, 2015

Because of the steric hindrance with the methyl connected to the carbonyl C=O group.

Explanation:

N,N-dimethylacetamide.

My best guess would be that the two methyl groups on the nitrogen atom restrict the rotation around the C−N bond because of the steric hindrance with the methyl connected to the carbonyl C=O group.
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Acetamide.

However, we can see that there is more room around the nitrogen atom in the case of acetamide:
enter image source here

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