Match each organic nitrogen compound on the left with its corresponding relative basicity … — JAMB UTME

Match each organic nitrogen compound on the left with its corresponding relative basicity or acid-base structural property on the right.

Phenylamine ( $C_6H_5NH_2$ )Weaker base than ammonia ( $NH_3$ ) because the unshared electron pair is delocalized over the aromatic ring.
Methylamine ( $CH_3NH_2$ )Stronger base than ammonia ( $NH_3$ ) due to the positive inductive effect (+I) of a single alkyl group.
Ethanamide ( $CH_3CONH_2$ )Essentially neutral in aqueous solution because the nitrogen lone pair is resonance-delocalized into the carbonyl group.
Dimethylamine ( $(CH_3)_2NH$ )Stronger base than methylamine in aqueous solution due to the electron-donating effect of two alkyl groups.

Answer

Phenylamine matches with being weaker than ammonia due to aromatic delocalization; Methylamine matches with being stronger than ammonia due to +I inductive effect; Ethanamide matches with being neutral due to carbonyl resonance; Dimethylamine matches with being stronger than methylamine in aqueous solution.

Phenylamine is less basic than ammonia because its lone pair is delocalized across the aromatic ring. Methylamine is more basic than ammonia due to inductive electron donation by the methyl group. Ethanamide is neutral because its lone pair participates in resonance with the carbonyl group. Dimethylamine is more basic than methylamine in water due to two electron-donating methyl groups.

Step-by-Step Solution

Analyze how structural features influence nitrogen lone pair availability.

Electron-donating alkyl groups (+I effect) enhance lone pair availability (increasing basicity), while electron-withdrawing groups or resonance delocalization decrease lone pair availability (decreasing basicity).

Lewis/Brønsted-Lowry basicity of nitrogen compounds depends directly on lone pair availability to accept a proton.

Evaluate phenylamine and ethanamide.

Phenylamine delocalizes its lone pair into the benzene ring, making it weaker than

NH_3

. Ethanamide delocalizes its lone pair into the

C=O

double bond, making it neutral in aqueous solution.

Resonance delocalization significantly stabilizes the unprotonated state and lowers basicity.

Compare methylamine and dimethylamine.

Methylamine has one alkyl group increasing basicity over

NH_3

. Dimethylamine has two alkyl groups supplying greater electron density, making it more basic than methylamine in aqueous solution.

Inductive electron donation by methyl groups stabilizes the positive conjugate ammonium ion.

Key Concept

Relative basicity of amines and amides based on inductive and resonance effects

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