Isomers of hexane, based on their branching, can be divided into three distinct classes as shown in the figure.
I
II
III
The correct order of their boiling point is
(A)I > II > III
(B)III > II > I✓ Correct
(C)II > III > I
(D)III > I > II
Answer: (B)
Solution
Boiling point decreases with increasing branching in alkanes. This is because branching reduces the surface area available for van der Waals interactions between molecules. Class III (straight-chain hexane) has the highest boiling point due to maximum surface contact. Class II (moderately branched) has intermediate boiling point. Class I (highly branched) has the lowest boiling point. Therefore, the order is III > II > I.
JEE Advanced · 2014 · 25 May 2014 · Paper 2 · Single correct option
