Question

The correct order of boiling points of compounds I–IV is 

• A. II > I > III > IV
• B. II > III > I > IV
• C. I > III > IV > II
• D. I > IV > III > II

Hint:

Boiling points are typically higher for larger molecules and those with stronger intermolecular forces like hydrogen bonding.

Answer 1

The Correct Option is C

To determine the order of boiling points for the given compounds, we must consider the factors affecting the boiling points, such as hydrogen bonding, molecular weight, and branching.

1. Compound I: Butanol
   This compound can form hydrogen bonds due to the presence of the -OH group. It is a straight-chain alcohol, which generally results in a higher boiling point compared to branched alcohols.
2. Compound II: Diethyl Ether
   Although ethers have dipole-dipole interactions, they cannot form hydrogen bonds like alcohols. This means their boiling points are lower than alcohols of similar molecular mass.
3. Compound III: Isopropanol
   This is a secondary alcohol that forms hydrogen bonds. Due to the branching, its boiling point is lower compared to the straight-chain butanol (Compound I). However, it is higher than ether due to hydrogen bonding.
4. Compound IV: 2-Propanol
   Similar to isopropanol, but as a primary alcohol, it can engage in effective hydrogen bonding. Its molecular size is slightly smaller than butanol, which reduces its boiling point compared to butanol but still higher than the diethyl ether.

Based on these observations, the correct order of boiling points from highest to lowest is:

• I > III > IV > II

This is because Compound I, being a straight-chain alcohol with strong hydrogen bonding and no branching, has the highest boiling point. Compound III, although branched, still forms hydrogen bonds effectively, followed by Compound IV. Lastly, Compound II, lacking hydrogen bonding, has the lowest boiling point.