Question

Which of the following amine has the highest boiling point?

• A. \(CH_3CH_2NH_2\)
• B. \(CH_3CH_2CH_2CH_2NH_2\)
• C. \((C_2H_5)_2NH\)
• D. \((CH_3)_2NC_2H_5\)
• E. \(CH_3CH_2CH_2NH_2\)

Hint:

Boiling Point Order: Primary Amine \(>\) Secondary Amine \(>\) Tertiary Amine (for similar mass).
Within primary amines: Boiling Point \(\propto\) Molecular Mass.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The boiling point of amines depends on two main factors: intermolecular hydrogen bonding and molecular mass (Van der Waals forces).
Primary amines (\(RNH_2\)) have two hydrogen atoms available for H-bonding, secondary amines (\(R_2NH\)) have one, and tertiary amines (\(R_3N\)) have none.

Step 3: Detailed Explanation:
1. H-Bonding: Primary amines generally have higher boiling points than secondary and tertiary amines of comparable molecular mass because they can form more hydrogen bonds.
2. Molecular Mass: For a given type of amine (e.g., primary), the boiling point increases with the increase in molecular mass because the magnitude of Van der Waals forces increases.
- Option (A) is ethylamine (\(C_2\)).
- Option (E) is propylamine (\(C_3\)).
- Option (B) is n-butylamine (\(C_4\)).
Since all three are primary amines, n-butylamine (B) has the highest molecular mass and thus the highest boiling point.
- Options (C) and (D) are secondary and tertiary amines respectively, which have weaker intermolecular attractions compared to primary amines of similar mass.

Step 4: Final Answer:
The amine with the highest boiling point is \(CH_3CH_2CH_2CH_2NH_2\) (n-butylamine).