Question

The correct order of decreasing basic strength of the given amines is:

• A. N-ethylmethanamine $>$ ethanamine $>$ benzenamine $>$ N-methylaniline
• B. N-ethylmethanamine $>$ ethanamine $>$ N-methylaniline $>$ benzenamine
• C. N-methylaniline $>$ ethanamine $>$ benzenamine $>$ N-ethylmethanamine
• D. N-methylaniline $>$ N-ethylmethanamine $>$ benzenamine $>$ ethanamine

Hint:

When evaluating the basicity of amines, remember that alkyl groups increase basicity by donating electron density, while aromatic rings decrease basicity by withdrawing electron density.

Answer 1

The Correct Option is B

The fundamental basicity of amines is contingent on the availability of the nitrogen lone pair for protonation. Electron-donating and electron-withdrawing substituents bonded to the nitrogen atom influence amine basicity. The general principles are as follows:
- Alkyl groups (e.g., ethyl, methyl) enhance nitrogen's electron density, thereby increasing its basicity.
- A benzene ring (as observed in benzenamine) exerts an electron-withdrawing influence via resonance, consequently reducing nitrogen's basicity.
Analysis of the amines presented in the options is as follows:
- N-ethylmethanamine (ethylamine): The ethyl group, being electron-donating, renders the nitrogen more basic compared to ethanamine.
- Ethanamine (ethylamine): The amine group is attached to an ethyl group, providing significant electron-donating effects, albeit less pronounced than in N-ethylmethanamine.
- N-methylaniline: While the methyl group is electron-donating, the benzenamine's aromatic ring withdraws electron density through resonance, resulting in N-methylaniline exhibiting lower basicity than ethanamine.
- Benzenamine (aniline): The aromatic ring exerts a potent electron-withdrawing effect on the nitrogen, establishing it as the least basic among all options.

Consequently, the established order of basicity is N-ethylmethanamine $>$ ethanamine $>$ N-methylaniline $>$ benzenamine.