Question

Arrange the following compounds in increasing order of their boiling point: \[ \text{(CH}_3\text{)}_2\text{NH, CH}_3\text{CH}_2\text{NH}_2, \text{CH}_3\text{CH}_2\text{OH} \] 

Hint:

Boiling points increase with the strength of intermolecular forces. Alcohols have stronger hydrogen bonding than amines, which leads to higher boiling points.

Answer 1

Order of Boiling Points Based on Intermolecular Forces 

To determine the increasing order of boiling points of the given compounds, we analyze the nature and strength of their intermolecular forces:

1. Dimethylamine \((\text{CH}_3)_2\text{NH}\):
   - A secondary amine that exhibits weak hydrogen bonding.
   - Possesses dipole-dipole interactions and van der Waals forces.
   - However, hydrogen bonding is not as effective as in alcohols.
   - Thus, it has the lowest boiling point among the three.
2. Ethylamine \(\text{CH}_3\text{CH}_2\text{NH}_2\):
   - A primary amine capable of forming stronger hydrogen bonds than dimethylamine.
   - Also exhibits dipole-dipole interactions.
   - Slightly higher boiling point due to a larger ethyl group, which increases van der Waals forces.
3. Ethanol \(\text{CH}_3\text{CH}_2\text{OH}\):
   - An alcohol with a hydroxyl group capable of forming strong hydrogen bonds.
   - Hydrogen bonding in alcohols is typically stronger than in amines.
   - Therefore, ethanol has the highest boiling point.

Conclusion:

The order of increasing boiling points is:

\(( CH 3 ) 2 NH < CH 3 CH 2 NH 2 < CH 3 CH 2 OH (CH 3 ​ ) 2 ​ NH\)