Question

Assertion (A): Boiling point of propylamine is higher than that of trimethylamine.
Reason (R): In propylamine, intermolecular hydrogen bonding occurs, whereas trimethylamine does not undergo intermolecular hydrogen bonding.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

For isomeric amines, the boiling point order is: Primary $\gt $ Secondary $\gt $ Tertiary, directly correlating to the number of available N-H bonds.

Answer 1

The Correct Option is A

Step 1: Identify the structural difference between the two amines.
Propylamine ($CH_3CH_2CH_2NH_2$) is a primary amine with two N-H bonds. Trimethylamine ($(CH_3)_3N$) is a tertiary amine with zero N-H bonds; all three bonds on nitrogen are N-C bonds.
Step 2: Determine hydrogen bonding capacity.
Intermolecular hydrogen bonding in amines requires an N-H bond acting as a hydrogen bond donor. Propylamine can form $N$-$H \cdots N$ hydrogen bonds with adjacent molecules. Trimethylamine cannot form N-H hydrogen bonds with itself.
Step 3: Connect to boiling point.
The hydrogen bond network in liquid propylamine requires additional energy to break, raising its boiling point significantly above that of trimethylamine, which is held together only by weaker London dispersion forces.
Step 4: Assess assertion and reason.
The assertion (propylamine has a higher boiling point) is true. The reason (propylamine has intermolecular H-bonding while trimethylamine does not) is true and correctly explains the assertion.
\[ \boxed{\text{Both A and R are true; R is the correct explanation of A}} \]