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

Boiling Point Order Based on Intermolecular Forces

The increasing order of boiling points for the given compounds is determined by analyzing their intermolecular forces:

1. Dimethylamine \((\text{CH}_3)_2\text{NH}\):
   - Classified as a secondary amine, it exhibits weak hydrogen bonding.
   - It also displays dipole-dipole interactions and van der Waals forces.
   - Hydrogen bonding in this compound is less effective compared to alcohols.
   - Consequently, it possesses the lowest boiling point among the three substances.
2. Ethylamine \(\text{CH}_3\text{CH}_2\text{NH}_2\):
   - As a primary amine, it can form stronger hydrogen bonds than dimethylamine.
   - Dipole-dipole interactions are also present.
   - The presence of a larger ethyl group leads to increased van der Waals forces, resulting in a slightly higher boiling point.
   
3. Ethanol \(\text{CH}_3\text{CH}_2\text{OH}\):
   - Identified as an alcohol, its hydroxyl group enables the formation of strong hydrogen bonds.
   - Hydrogen bonding in alcohols is generally more robust than in amines.
   - Therefore, ethanol exhibits the highest boiling point.

Conclusion:

The sequence of increasing boiling points is:

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