1.Why is the boiling point of 3-methylheptane (bp 118 oC) less than that of n-oc

Question

1.Why is the boiling point of 3-methylheptane (bp 118 oC) less than that of n-octane (bp 125 oC)?

A. n-octane has a greater molar mass. As molar mass increases so does boiling point

B. n-octane has more carbon atoms than 3-methylheptane. Compounds with a greater number of carbons tend to have higher boiling points

C. 3-methylheptane is a branched chain alkane while n-octane is straight chain. Branched chain molecules have lower boiling points because they cannot line up together for the intermolecular forces to be as effective.

D. 3-methylheptane is an alkene which tend to have lower boiling points than alkanes such as n-octane.

Explanation / Answer

The boiling point of an alkane reduces to a great extend if branching is present. For ex. the boiling point of n-pentane(309K) would be greater than isopentane(300K) which wil have greater boinling point than neopentane(282.5K). The suface area reduces and hence the boiling point decreases. Thus the answer to this question would be option (C).

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