Question

If branching increasing stability in alkanes (will have lower heat of combustion), then how does an increase in branching lead to lower boiling points?

Answer 1

The boiling point is related to the force between the molecules. In the case of hydrocarbons G.e. alkanes), it is the Van Der Waals interaction. In precise, it is the intermolecular attractive force. As this intermolecular attractive force decreases, boiling point decreases Branching of the alkane chain leads to decrease in the surface area of the molecule (i.e. branching makes the chain more compact). As the surface area decreases, the intermolecular attractive force also decreases which leads to lower in the boiling point.