Question: Which compound in each pair has the higher boiling point?

a.

b.

The point or the temperature at which the vapor pressure of the compound equals the atmospheric/surrounding pressure is termed the boiling point of the compound.

The boiling point of a compound depends on the following factors:

• The intermolecular forces: The stronger the intermolecular forces acting on a compound, the higher is its boiling point.
• The boiling point increases with the increase in the number of carbon atoms.
• Branching in the compounds: As the number of branches or the side chains in a compound increases, the boiling point of the compound decreases.
• The polarity of the compounds: Polar compounds have a higher boiling point than nonpolar compounds.

a.

Compounds in (a)

In the case of (a), the second compound has a higher boiling point as it contains more carbon atoms leading to a larger surface area and stronger intermolecular forces.

b.

The first compound (the one containing the iodine atom) has a higher boiling point as the carbon-iodine (C-I) bond is weak compared to the carbon-bromine (C-Br) bond due to the larger size of iodine compared to that of bromine.

Since the carbon-iodine bond is weak, it's highly polarizable.