Question

Arrange the following compounds in increasing order of their melting points.

• A. Butane
• B. Cis-2-butene
• C. Trans-2-butene
• D. Octane

Answer 1

Melting point increases with increasing polarity, surface area and packing efficiency of the molecules.

• Melting point of alkenes is higher than corresponding alkanes due to more polarisability of pi bond.
• Trans-2-butene has higher melting point than cis-2-butene because of better packing efficiency of trans alkenes.
• Octane has highest molar mass and surface area. Thus, van der Waals forces will be highest for octane among the given options.