Three structural isomers of C₅H₁₂—n-pentane, isopentane, and neopentane—have identical molecular formulas but different shapes.
Boiling points (experimentally determined):
• n-Pentane: 36 °C
• Isopentane: 28 °C
• Neopentane: 9 °C
Use these data to explore how molecular shape affects the magnitude of London dispersion forces.
(a) Re-rank the three isomers in order of increasing strength of London dispersion forces and explain how the experimental boiling-point data support your ranking.
(b) Identify the structural feature that most directly controls the variation in London dispersion forces among the three isomers, and describe at the particulate level how this feature influences the contact area available for intermolecular interactions.
(c) Suppose a hypothetical isomer of C₅H₁₂ could be synthesized that is perfectly linear and longer than n-pentane (i.e., with no branching at all). Predict qualitatively how its boiling point would compare with that of n-pentane and justify your prediction.