i may be wrong but Use the normal boiling points: propane, C3H8, –42.1˚C; butane, C4H10, –0.5˚C; pentane, C5H12, 36.1˚C; hexane, C6H14, 68.7˚C; heptane, C7H16, 98.4˚C; to estimate the normal boiling point of octane, C8H18.
Propane (C₃H₈) is symmetrical and non-polar, so the only inter-molecular forces are London dispersion forces.
Butane (C₄H₁₀) is symmetrical and non-polar, so the only inter-molecular forces are also London dispersion forces.
The only difference is the size. Butane has more atoms, more surface area, and therefore more inter-molecular forces. So it has a higher boiling point.
