Question 1

Why are amines nucleophilic?

Accepted Answer

The nitrogen atom of an amine has a lone pair that can be donated to an electron-deficient centre. This lone pair is responsible for the basic and nucleophilic character of primary, secondary and tertiary amines.

Question 2

What is the product of the first methylation of methylamine?

Accepted Answer

The first SN2 reaction between CH3NH2 and CH3Br forms [(CH3)2NH2]+ Br-. Nitrogen now has two methyl groups and two hydrogens, so this is a secondary ammonium salt rather than a quaternary ammonium salt.

Question 3

How is a quaternary ammonium salt formed by alkylation?

Accepted Answer

After proton removal and repeated SN2 methylation, methylamine can ultimately form [N(CH3)4]+ Br-. In general, R3N + R'X → [R3NR']+ X-.

Question 4

What happens when methylamine reacts with an acid chloride?

Accepted Answer

The nitrogen lone pair attacks the carbonyl carbon of CH3COCl, chloride is expelled, and the amide CH3CONHCH3 is formed. This compound is N-methylethanamide, and a base normally captures the proton during the reaction.

Question 5

Why is an amide less basic than an amine?

Accepted Answer

In an amide, the nitrogen lone pair is delocalised into the carbonyl group by resonance. This reduces the electron density available on nitrogen, so the amide is less basic than the corresponding amine.

Reactions at the Nitrogen Lone Pair

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Practice