Question

Identify the correct order of boiling points of the following compounds:
1. $C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH$
2. $C{H}_{3}C{H}_{2}C{H}_{2}CHO$
3. $C{H}_{3}C{H}_{2}C{H}_{2}COOH$

• A. $1>2>3$
• B. $3>1>2$
• C. $1>3>2$
• D. $3>2>1$

Answer 1

The correct option is B $3>1>2$

The boiling point of organic compounds depends on two factors:
i) Molecular weight: boiling point increases with increase in molecular weight.
ii) Intermolecular forces: higher the strengh of intermolecular forces, higher is the boiling point.

Butanoic acid forms extensive intermolecular hydrogen bonding than butanol. Carboxylic acids have the ability of forming a dimer by hydrogen bonding that leads to a stable arrangement. Hence, they have higher boiling points.
Butanal has a lower boiling point than the two due to comparitively weaker dipole-dipole interactions.