Which of the following has the highest boiling point ? (i)2-methylpentane, (ii)2,3-dimethylbutane , (iii)2,2-dimethylbutane.

Which of the following has the highest boiling point ? (i)2-methylpen

1.	Which of the following has the highest boiling point ? (i)2-methylpentane, (ii)2,3-dimethylbutane , (iii)2,2-dimethylbutane.
Answer» Solution :As the branching INCREASES , surface area decreases. As a result, magnitude of van der WAALS forces of attraction decreases and hence the boiling point decreases. Now 2-methylpentane has the largest surface area and hence has the highest boiling point. Further because of the presence of two BRANCHES on the same carbon, 2,2-dimethylbutane has LOWER surface area and hence has lower boiling point than that of 2,3-dimethylbutane. Thus, the overall order of decreasing boiling points is : 2-methylpentane (333 K) gt 2,3- dimethylbutane (331 K) gt 2,2-dimethylbutane (323 K)