Isomers of hexane, based on their degree of branching, have different boiling points. What is the correct descending order of boiling point for n-hexane (I), 2-methylpentane (II), and 2,2-dimethylbuta

Question

Isomers of hexane, based on their degree of branching, have different boiling points. What is the correct descending order of boiling point for n-hexane (I), 2-methylpentane (II), and 2,2-dimethylbutane (III)?

Prashant Kotian · Accepted Answer

Correct answer: A. The boiling point of alkanes decreases with increased branching. Branching makes the molecule more spherical, decreasing the effective surface area for intermolecular van der Waals dispersion forces. Thus, the unbranched n-hexane (I) has the highest boiling point, followed by the singly branched 2-methylpentane (II), and the doubly branched 2,2-dimethylbutane (III) has the lowest.

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