Problem

Both molecules are four-carbon chains with similar molar masses, so the key difference lies in what kinds of intermolecular forces they can form. Butan-1-ol has a hydroxyl group ($-\text{OH}$) that enables hydrogen bonding—a particularly strong intermolecular force—while butanal only has a carbonyl group ($\text{C}=\text{O}$) that can accept hydrogen bonds but not donate them. Since hydrogen bonding is significantly stronger than the dipole–dipole interactions that butanal relies on, butan-1-ol requires more energy to overcome these forces and escape into the gas phase, resulting in a higher boiling point.

Both molecules are four-carbon chains with similar molar masses, so the key difference lies in what kinds of intermolecular forces they can form. Butan-1-ol has a hydroxyl group ($-\text{OH}$) that enables hydrogen bonding—a particularly strong intermolecular force—while butanal only has a carbonyl group ($\text{C}=\text{O}$) that can accept hydrogen bonds but not donate them. Since hydrogen bonding is significantly stronger than the dipole–dipole interactions that butanal relies on, butan-1-ol requires more energy to overcome these forces and escape into the gas phase, resulting in a higher boiling point.