For isomeric alkyl halides, the boiling points decreases with branching. Branching of the chain makes the molecule more compact and therefore, the surface area decreases. Hence, the intermolecular attractive forces which depend upon the surface area, also become small in magnitude due to branching. Consequently, the boiling points of the branched chain having same molecular formula are less than the straight chain isomers. Higher the molecular weight, higher is the boiling point, but branching reduces boiling point.