Question

Give plausible explanation for each of the following:
Amides are less basic than amines.

Hint:

The basicity of amines is higher than amides because the lone pair on the nitrogen in amides is less available due to resonance with the carbonyl group.

Answer 1

To solve the problem, we need to explain why amides are less basic than amines.

1. Understanding Basicity:
Basicity refers to a compound's ability to accept protons (H⁺). The more readily a compound can donate its lone pair of electrons to bond with a proton, the more basic it is. In general, the basicity of nitrogen-containing compounds like amines and amides depends on the electron density around the nitrogen atom, as it is the site of protonation.

2. Structure of Amines:
Amines (R-NH₂) have a nitrogen atom with a lone pair of electrons. This lone pair is readily available for protonation, making amines relatively basic. The nitrogen in amines is not involved in any resonance structures that significantly reduce its electron density, allowing it to readily accept a proton.

3. Structure of Amides:
Amides (R-CO-NH₂) contain a carbonyl group (C=O) attached to a nitrogen atom. The nitrogen in amides is involved in resonance with the carbonyl group. This resonance delocalizes the lone pair of electrons on the nitrogen, making it less available for protonation. The carbonyl oxygen pulls electron density away from the nitrogen, which significantly reduces the nitrogen's ability to accept a proton.

4. Effect of Resonance on Basicity:
In amides, the resonance between the nitrogen's lone pair and the carbonyl group weakens the nitrogen's electron density, making it less basic. In contrast, amines do not experience this resonance effect, so the nitrogen’s lone pair remains more available for protonation, making them more basic.

5. Final Answer:
Amides are less basic than amines because the nitrogen in amides is involved in resonance with the carbonyl group, which reduces the availability of the nitrogen's lone pair for protonation. In contrast, the nitrogen in amines is not involved in such resonance and retains a higher electron density, making amines more basic.