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Difficulty: Very hardAmines and Amides: Structure, Basicity, and Reactions

Match each nitrogen-containing organic compound on the left with the statement on the right that accurately accounts for its aqueous basicity and lone-pair electronic behavior.

  • Dimethylamine, (CH3)2NH(CH_3)_2NHExhibits higher aqueous basicity than ammonia owing to +I+I inductive electron donation combined with favorable conjugate acid solvation.
  • Phenylamine, C6H5NH2C_6H_5NH_2Exhibits substantially lower basicity than aliphatic amines because the nitrogen lone pair delocalizes into the aromatic π\pi-system.
  • Ethanamide, CH3CONH2CH_3CONH_2Neutral in aqueous solution because the nitrogen lone pair is strongly delocalized by resonance into an adjacent carbonyl group.
  • Triethylamine, (C2H5)3N(C_2H_5)_3NExhibits lower aqueous basicity than its secondary aliphatic analogue due to steric hindrance restricting hydration of its conjugate acid.

Answer

Dimethylamine matches the statement describing higher aqueous basicity than ammonia due to inductive donation and solvation; Phenylamine matches the statement describing reduced basicity from aromatic resonance delocalization; Ethanamide matches the statement describing neutrality caused by carbonyl resonance; Triethylamine matches the statement describing steric hindrance affecting conjugate acid solvation.
The correct matches reflect fundamental physical-organic chemistry principles governing nitrogen basicity: Dimethylamine combines inductive donation with high conjugate acid solvation stability; Phenylamine suffers basicity loss from aromatic resonance delocalization; Ethanamide lone-pair delocalization into the carbonyl group yields a neutral compound; Triethylamine basicity in water is moderated by steric crowding that interferes with hydration of the ammonium cation.

Step-by-Step Solution

1
Analyze the electronic structure of Dimethylamine ((CH3)2NH(CH_3)_2NH).
Two methyl groups supply electron density via +I+I inductive effects, enhancing nitrogen lone-pair availability, while the secondary cation remains readily solvated by water.
Secondary aliphatic amines are generally the strongest bases in aqueous media.
2
Analyze the resonance interactions in Phenylamine (C6H5NH2C_6H_5NH_2).
The unshared electron pair on nitrogen participates in resonance with the benzene ring, lowering lone-pair availability.
Aromatic amines are significantly weaker bases than ammonia and aliphatic amines.
3
Examine the functional group characteristics of Ethanamide (CH3CONH2CH_3CONH_2).
Resonance delocalization between nitrogen's lone pair and the adjacent C=OC=O double bond (O=C−N↔−O−C=N+O=C-N \leftrightarrow ^-O-C=N^+) deprives nitrogen of basic character.
Amides behave as neutral organic compounds in aqueous solution.
4
Evaluate steric effects in Triethylamine ((C2H5)3N(C_2H_5)_3N).
Three ethyl groups create steric crowding around the nitrogen cation, hindering stabilization through hydration in water.
In aqueous solution, tertiary aliphatic amines are often weaker bases than secondary aliphatic amines due to solvation factors.

Key Concept

Relative basicity of aliphatic amines, aromatic amines, and amides governed by inductive, resonance, and solvation steric effects.
Estimated Time:2m 0s
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Topics

Amines and Amides: Structure, Basicity, and Reactions

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