Compared to amines, amides are very weak bases. While the conjugate acid of an amine has a pK of about 9.5, the conjugate acid of an amide has a pK around −0.5. Therefore, compared to amines, amides do not have acid–base properties that are as noticeable in water. This relative lack of basicity is explained by the withdrawing of electrons from the amine by the carbonyl. On the other hand, amides are much stronger bases than carboxylic acids, esters, aldehydes, and ketones (their conjugate acids pK's are between −6 and −10).
The proton of a primary or secondary amide does not dissociate readily; its pK is usually well above 15. Conversely, under extremely acidic conditions, the carbonyl oxygen can become protonated with a pK of roughly −1. It is not only because of the positive charge on the nitrogen but also because of the negative charge on the oxygen gained through resonance.