Arrange the following molecules from lowest to highest boiling point. (LO 8.9) (I)
(II)
(III)
(IV)
(a) I 6 II 6 III 6 IV (b) II 6 III 6 I 6 IV (c) IV 6 II 6 III 6 I (d) IV 6 I 6 II 6 III

Key Concepts

Boiling Point and Intermolecular Forces

The boiling point of a substance is influenced by the strength of its intermolecular forces. Stronger forces, such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces, lead to higher boiling points. Molecules with significant hydrogen bonding, like alcohols, typically have higher boiling points compared to non-polar molecules or those with weaker interactions.

Molecular Structure and Polarity

The molecular structure, including the presence of functional groups and the overall shape, affects polarity. Polar molecules, which have an uneven distribution of charge, tend to have higher boiling points due to stronger dipole-dipole interactions. In contrast, non-polar molecules primarily exhibit London dispersion forces, which are generally weaker.

Hydrogen Bonding

Hydrogen bonding is a specific type of strong dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. This interaction significantly increases the boiling point of compounds containing -OH groups, as seen in alcohols, compared to hydrocarbons that lack such polar functional groups.