Question

Out of 2-Methylbutane and 2,2-Dimethylpropane which will have higher boiling point and why ?​

Answer 1

Explanation:

Boiling point increases with increase in molecular mass. For the compounds with the same molecular mass, boiling point decreases with an increase in branching.

The molecular mass of 2-Methylbutane: 72gmol

−1

The molecular mass of 2-Methylpropane: 58gmol

−1

The molecular mass of 2,2-Dimethylpropane: 72gmol

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The molecular mass of 2-Methylbutane: 72gmol

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2-Methylpropane has the lowest molecular mass among all of the given compounds.

Thus, 2-Methylpropane has the lowest boiling point among the given options.

Answer 2

Question:-

Out of 2-Methylbutane and 2,2-Dimethylpropane which will have higher boiling point and why ?

Answer:-

Amongst isomeric alkanes, the branched chain isomer has the lower boiling point than the corresponding n-alkane. This is due to the reason that with branching the shape of the molecule tends to approach that of a sphere. As a result, the surface area of the branched isomer decreases. Due to lesser surface area of these molecules, the van der Waals forces of attraction operating between their molecules become comparatively weaker and hence lesser amount of energy is required to overcome then. Thus the order of boiling points of chain isomers of pentane:

CH3CH2CH2CH2CH3n−pentane(b.p.=309.1 K)>CH3−CHCH3|−CH2CH32−methylbutane(b.p. = 301 K) CH3−CCH3||CH3−CH32, 2−dimethylpropane(b.p. = 282.5 K)

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