Boiling Point Order Analysis

The boiling point of a substance depends primarily on the strength of the intermolecular forces (IMFs) holding its molecules together. Overcoming stronger IMFs requires more energy, leading to higher boiling points.

Intermolecular Forces Comparison

Let's analyze the IMFs present in each compound:

• n-Butane (C₄H₁₀): A nonpolar alkane. Only has weak London dispersion forces.
• Ethoxyethane (C₂H₅OC₂H₅): An ether. Exhibits London dispersion forces and weaker dipole-dipole interactions due to the polar C-O bond.
• Pentanal (C₄H₉CHO): An aldehyde. Has London dispersion forces and stronger dipole-dipole interactions because of the highly polar carbonyl group (C=O).
• Pentan-1-ol (C₅H₁₁OH): An alcohol. Possesses London dispersion forces, dipole-dipole interactions, and crucially, strong hydrogen bonding due to the -OH group.

Boiling Point Trend

The general order of IMF strength is:

London Dispersion Forces < Dipole-Dipole Interactions < Hydrogen Bonding

Applying this to the given compounds:

1. n-Butane has the weakest IMFs, hence the lowest boiling point.
2. Ethoxyethane has stronger IMFs than n-Butane due to dipole-dipole forces.
3. Pentanal has stronger dipole-dipole interactions than Ethoxyethane because the carbonyl group is more polar.
4. Pentan-1-ol has the strongest IMFs due to hydrogen bonding, giving it the highest boiling point.

Therefore, the correct order of increasing boiling points is:

n-Butane < Ethoxyethane < Pentanal < Pentan-1-ol