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Difficulty: EasyAmines and Amides: Structure, Basicity, and Reactions

Which of the following organic compounds acts as a weak base in an aqueous solution due to the presence of an unshared pair of electrons on its nitrogen atom?

  1. Methylamine (CH3NH2CH_3NH_2)Answer
  2. B
    Ethanamide (CH3CONH2CH_3CONH_2)
  3. C
    Ethanoic acid (CH3COOHCH_3COOH)
  4. D
    Ethanol (CH3CH2OHCH_3CH_2OH)

Answer

Methylamine (CH3NH2CH_3NH_2)
Methylamine (CH3NH2CH_3NH_2) is an aliphatic amine. The nitrogen atom retains a localized lone pair of electrons that readily accepts a proton from water to form a methylammonium ion and a hydroxide ion, demonstrating basic behavior in aqueous solution.

Step-by-Step Solution

1
Identify the functional groups present in each compound.
Methylamine (CH3NH2CH_3NH_2) is an amine; ethanamide (CH3CONH2CH_3CONH_2) is an amide; ethanoic acid (CH3COOHCH_3COOH) is a carboxylic acid; ethanol (CH3CH2OHCH_3CH_2OH) is an alcohol.
Basic properties in organic nitrogen compounds depend on the availability of the nitrogen lone pair.
2
Evaluate the availability of the unshared pair of electrons on the nitrogen atom.
In primary aliphatic amines like methylamine, the lone pair on nitrogen is readily available to accept a proton (H+H^+). In amides like ethanamide, resonance delocalizes the nitrogen lone pair toward the carbonyl oxygen, removing its basic character.
Proton acceptance (Lewis/Brønsted-Lowry basicity) requires an available lone pair.

Key Concept

Basicity of Amines versus Amides
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Topics

Amines and Amides: Structure, Basicity, and Reactions

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