Question

Which among the following has the highest boiling point?

• A. Propanone
• B. Propan-1-ol
• C. Ethanoic acid
• D. Propanal

Hint:

The presence of hydrogen bonding significantly increases the boiling point of a compound, as seen in alcohols and carboxylic acids.

Answer 1

The Correct Option is C

Step 1: Boiling point and intermolecular forces.
The boiling point of a substance depends on the strength of the intermolecular forces between its molecules. Stronger intermolecular forces require more energy (heat) to overcome, leading to a higher boiling point. The main intermolecular forces in organic compounds are van der Waals forces (dispersion forces), dipole-dipole interactions, and hydrogen bonding.

Step 2: Analyze the compounds.
- Propanone (Acetone): It is a ketone, with van der Waals forces and dipole-dipole interactions, but no hydrogen bonding. It is expected to have a moderate boiling point.
- Propan-1-ol: It is an alcohol, which can form hydrogen bonds between molecules. This significantly increases its boiling point compared to molecules that only experience van der Waals forces.
- Ethanoic acid (Acetic acid): It is a carboxylic acid, and like alcohols, it can form hydrogen bonds. However, in addition to this, carboxylic acids can also form dimeric structures (two molecules bonding together) through strong hydrogen bonding, further increasing the boiling point.
- Propane (Propanal): It is an aldehyde, which has weaker dipole-dipole interactions than alcohols or carboxylic acids and no possibility for hydrogen bonding like alcohols. Hence, it is expected to have the lowest boiling point among the options.

Step 3: Conclusion.
Among the given compounds, ethanoic acid, with its strong hydrogen bonding and ability to form dimers, will have the highest boiling point. Therefore, the correct answer is:
\[ \boxed{\text{(C) Ethanoic acid}} \]