What happens to the boiling point of isomers with the same relative mass as the degree of branching increases?

As the degree of branching increases among isomers with the same relative mass, the boiling point typically decreases. This trend is explained by the molecular structure and intermolecular forces at play.

In straight-chain isomers, the molecules can pack more closely together, resulting in stronger London dispersion forces due to greater surface area contact between molecules. These stronger forces require more energy to overcome, leading to a higher boiling point.

On the other hand, with branched isomers, the branching disrupts the packing of the molecules, reducing the surface area available for intermolecular interactions. Consequently, the weakened London dispersion forces between the branched molecules require less energy to break, resulting in a lower boiling point compared to their straight-chain counterparts.

This relationship highlights how molecular geometry significantly influences physical properties such as boiling point, especially in isomers with identical molecular weights.