Hydrogen bonding in ethanol yields the highest boiling point

Steps:

• Identify functional groups: Ethanol (CH3CH2OH) and methanol (CH3OH) contain -OH groups enabling hydrogen bonding; methoxymethane (CH3OCH3) is an ether with only dipole-dipole forces.
• Compare forces: Hydrogen bonds are stronger than permanent dipole-dipole forces, so methoxymethane has the lowest boiling point.
• Compare alcohols: Both form hydrogen bonds, but ethanol's larger molecular weight (46 g/mol vs. methanol's 32 g/mol) increases London dispersion forces, raising its boiling point above methanol's.
• Confirm values: Ethanol boils at 78°C, methanol at 65°C, methoxymethane at -24°C.

Why C is correct:

• Ethanol exhibits hydrogen bonding (O-H···O), the strongest intermolecular force here, combined with its size for the highest boiling point.

Why the others are wrong:

• A: Methoxymethane lacks hydrogen bonding, relying on weaker dipole-dipole forces for its low boiling point.
• B: Methanol forms hydrogen bonds but has lower molecular weight, resulting in a boiling point below ethanol's.
• D: Ethanol's dominant force is hydrogen bonding, not just permanent dipole-dipole forces.

Final answer: C