Among the following select the alkane that is expected to have lowest boiling point

Options

A. Hexane
B. 2-methylpentane
C. 3-methylpentane
D. 2,2-dimethylbutane

Answer

D

Explanation

As the number of carbon atom increases, the boiling points of alkane increases because van der Waals' forces increases. However, branching results in decrease in boiling point due to decreased surface area which results in weaker van der Waals' forces. Thus, order of boiling points of given alkanes is
`CH_(3)-CH_(2)-underset("Hexane")(CH_(2)-CH_(2)-CH_(3)-CH_(3)gt`
`CH_(3)-CH_(2)-underset(2-"methylpentane")(CH_(2))-overset(CH_(3))overset(|)(C)H-CH_(3)gt`
`CH_(3)-CH_(2)-underset("methylpentane")overset(CH_(3))overset(|)(C)H-CH_(2)-CH_(3)gt`
`CH_(3)-underset(2,2"dimethylbutane")overset(CH_(3))overset(|)(C)H-CH_(3)`