Clear All CH3CH2CCH2CH2CH3 Lowest boiling point CH3CH2CH2CH2CH2CH2OH Intermediate boiling point Highest boiling point CH3CH2CH2CH2C-OH
The Correct Answer and Explanation is:
To rank the compounds from lowest to highest boiling point, let’s identify and analyze each structure:
- CH₃CH₂C≡CHCH₂CH₃ → This is hex-2-yne, an alkyne with a linear structure.
- CH₃CH₂CH₂CH₂CH₂CH₂OH → This is hexanol, a primary alcohol.
- CH₃CH₂CH₂CH₂COOH → This is pentanoic acid, a carboxylic acid.
Correct Ranking by Boiling Point:
Lowest boiling point: CH₃CH₂C≡CHCH₂CH₃ (hex-2-yne)
Intermediate boiling point: CH₃CH₂CH₂CH₂CH₂CH₂OH (hexanol)
Highest boiling point: CH₃CH₂CH₂CH₂COOH (pentanoic acid)
Explanation:
Boiling point depends on the strength of intermolecular forces. The stronger the forces, the higher the boiling point. The three main types of intermolecular forces are:
- London dispersion forces (weakest)
- Dipole-dipole interactions
- Hydrogen bonding (strongest of the three)
Let’s evaluate each compound:
- CH₃CH₂C≡CHCH₂CH₃ (hex-2-yne):
This compound has a triple bond and is nonpolar. The primary intermolecular force is London dispersion. It lacks groups like -OH or -COOH, so it cannot hydrogen bond. Therefore, it has the lowest boiling point.
- CH₃CH₂CH₂CH₂CH₂CH₂OH (hexanol):
Hexanol has a hydroxyl group (-OH), which allows for hydrogen bonding, increasing its boiling point. However, alcohols generally have lower boiling points than carboxylic acids because they form fewer hydrogen bonds per molecule.
- CH₃CH₂CH₂CH₂COOH (pentanoic acid):
Carboxylic acids have both a hydroxyl and a carbonyl group, allowing them to form strong dimeric hydrogen bonds. This makes their boiling points higher than alcohols and far higher than hydrocarbons or alkynes.
Conclusion:
The correct order from lowest to highest boiling point is:
CH₃CH₂C≡CHCH₂CH₃ < CH₃CH₂CH₂CH₂CH₂CH₂OH < CH₃CH₂CH₂CH₂COOH.
