Question

The following amines are having same molecular masses. (i) n-C\(_4\)H\(_9\)NH\(_2\) (ii) (C\(_2\)H\(_5\))\(_2\)NH (iii) C\(_2\)H\(_5\)N(CH\(_3\))\(_2\). The correct order of boiling point of the above amines is

• A. (i) $>$ (ii) $>$ (iii)
• B. (ii) $>$ (iii) $>$ (i)
• C. (iii) $>$ (i) $>$ (ii)
• D. (ii) $>$ (i) $>$ (iii)
• E. (i) $>$ (iii) $>$ (ii)

Hint:

For isomeric amines, the boiling point order is: 1\(^\circ\) $>$ 2\(^\circ\) $>$ 3\(^\circ\).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Boiling point of amines depends on the extent of hydrogen bonding. Primary amines have two H atoms for H-bonding, secondary have one, and tertiary have none.
Step 2: Detailed Explanation:
All three amines are isomers with the molecular formula C₄H₁₁N.
(i) n-C₄H₉NH₂: 1° amine. Has two H atoms on N, can form strong intermolecular H-bonds. Highest boiling point.
(ii) (C₂H₅)₂NH: 2° amine. Has one H atom on N, can form H-bonds, but weaker than 1° amine. Intermediate boiling point.
(iii) C₂H₅N(CH₃)₂: 3° amine. No H atom on N, cannot form H-bonds. Only weak London forces. Lowest boiling point. Order: Primary > Secondary > Tertiary.
Step 3: Final Answer:
The correct order is (i) > (ii) > (iii).