Four organic liquids are listed below. Normal boiling points are intentionally omitted.
1. n-Butane, C₄H₁₀ Molar mass = 58.1 g mol⁻¹ Dipole moment ≈ 0 D
2. Dimethyl ether, CH₃OCH₃ Molar mass = 46.1 g mol⁻¹ Dipole moment = 1.30 D
3. n-Pentane, C₅H₁₂ Molar mass = 72.2 g mol⁻¹ Dipole moment ≈ 0 D
4. Acetaldehyde, CH₃CHO Molar mass = 44.1 g mol⁻¹ Dipole moment = 2.70 D
Answer the questions that follow.
(a) Rank the four liquids from lowest to highest expected normal boiling point. Clearly indicate any ties.
(b) For each adjacent pair in your ranking, identify which intermolecular force (London dispersion or dipole–dipole) is primarily responsible for the difference in boiling point, and justify your choice with reference to specific molecular properties.
(c) Suppose each substance is instead examined as an amorphous solid at 90 K. For which one, if any, would the dominant intermolecular force differ from that identified in part (b)? Explain your reasoning.