Amides such as acetamide are much weaker bases than amines, such as ethylamine .
(a) Use resonance forms to show why the nonbonding electrons on the nitrogen atom of the amide are very weakly basic.
(b) Strong acid is required to protonate the amide. Predict where acetamide will undergo protonation, and use resonance forms to show why the site you have chosen is more basic. (Hint: To compare basicities, compare the stabilities of the conjugate acids.)
The structures of acetamide and ethyl amine are as follows:
The resonance structure of acetamide is as follows:
Here, the electron pair on N atom is not readily available to an acid for the protonation because the lone pairs involve in resonance stabilization.
Whereas, in ethyl amine there is no possibility for the resonance stabilization, so the lone pair of electrons on nitrogen atom are readily available for the protonation.
Therefore, the lone pair of electrons on the nitrogen atom in amide is weaker base.
There are two possibilities for the protonation of the amide: protonation on N and protonation on O.
The lone pair of electrons on nitrogen atom gets protonated and forms a protonated amide.
There is no possibility of resonance stabilization with this protonated amide. The reaction is as follows:
The lone pair of electrons on oxygen atom gets protonated and forms a resonance stabilized product. The reaction is as follows:
Therefore, protonation of amide on oxygen atom is more favorable than the protonation of nitrogen atom because of the resonance stabilization and makes the oxygen atom more basic than N atom.