Question

The correct order of increasing boiling points is

• A. n-butane < 1-butanol < n-butyl chloride < isobutane
• B. n-butane < isobutane < n-butyl chloride <1-butanol
• C. isobutane < n-butyl chloride < n-butane <1-butanol
• D. isobutane < n-butane < n-butyl chloride <1-butanol

Answer 1

Answer: (D)

Increase in branching decreases surface area of the molecule and hence, results lesser van der Waals' forces. Consequently, isobutane has lesser boiling point than $n$-butane.
Alkyl halides have higher boiling points than corresponding alkanes, because they are polar and stronger dipole-dipole force operate between the molecules of alkyl chloride. Alcohols have higher boiling point than their corresponding alkyl chloride, because alcohol molecules are associated through strong hydrogen bonds.