Question

Amines are usually formed from amides, imides, halides, nitro compounds, etc. They exhibit hydrogen bonding which influences their physical properties. In alkyl amines, a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia. Amines being basic in nature, react with acids to form salts. Aryldiazonium salts, undergo replacement of the diazonium group with a variety of nucleophiles to produce aryl halides, cyanides, phenols and arenes.

Why is the pK$_b$ value of aniline more than that of methylamine?

Hint:

Electron-donating groups such as alkyl groups increase the electron density on nitrogen, making the amine more basic, while electron-withdrawing groups like the phenyl group decrease basicity.

Answer 1

Aniline has a higher pK$_b$ value than methylamine because the amino group (-NH$_2$) in aniline is attached to a benzene ring, which exerts an electron-withdrawing effect through resonance. This reduces the electron density on nitrogen, making it less basic. In methylamine, the methyl group donates electrons to nitrogen, making it more basic and thus lowering its pK$_b$ value.