Question 1

Why are alkyl amines basic?

Accepted Answer

Alkyl amines are basic because the nitrogen lone pair can accept a proton to form an ammonium ion. Their alkyl groups exert a +I effect, which generally increases electron density on nitrogen, although solvation and steric effects influence the final aqueous basicity.

Question 2

Why is dimethylamine more basic than trimethylamine in water?

Accepted Answer

Dimethylamine has the lower pKb value, 3.27, compared with 4.22 for trimethylamine. Although alkyl groups donate electron density by the +I effect, trimethylamine has greater steric crowding and less favourable solvation in water.

Question 3

Why is aniline less basic than methylamine?

Accepted Answer

In aniline, the nitrogen lone pair occupies a p orbital and is conjugated with the benzene pi system. Delocalisation makes the lone pair less available for protonation, so aniline is much less basic than methylamine.

Question 4

What is the relationship between pKb and amine strength?

Accepted Answer

A lower pKb value means a stronger base. The methylamines have pKb values 3.36, 3.27 and 4.22, while aniline has a much higher pKb of 9.40 in this comparison.

Question 5

Does protonation of an amine destroy its basic character permanently?

Accepted Answer

No. Protonation is a reversible acid-base equilibrium. The ammonium ion can lose a proton later and return to the neutral amine, so the process is represented as B + H+ ↔ BH+.

Why Some Amines Are Stronger Bases

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