MCAT Chemical and Physical Foundations Practice Exam 2025 – Complete Study Guide

Carbonyl compounds exhibit a higher boiling point than alkanes primarily due to dipole interactions, which arise from the presence of a polar carbonyl functional group. The carbonyl group (C=O) has a significant difference in electronegativity between the carbon and oxygen atoms, creating a permanent dipole moment. This dipole leads to attractive forces between the carbonyl molecules that are stronger than the London dispersion forces present in alkanes.

In contrast, alkanes are nonpolar molecules and rely predominantly on weaker London dispersion forces for their intermolecular interactions. As the strength of the intermolecular forces directly influences boiling points, the stronger dipole-dipole interactions in carbonyls result in a higher boiling point compared to alkanes of similar molecular weight.

Understanding that electronegativity differences across atoms lead to polarity helps clarify why certain compounds have characteristic boiling points based on their functional groups.