Isomerisation of straight chain alkanes does not necessarily lower their boiling temperature. In fact, it often has the opposite effect, increasing the boiling point.

However, some isomers, including branched alkanes, may have lower boiling points compared to their straight-chain counterparts due to differences in molecular structure and intermolecular forces. Branched alkanes have a more compact shape and weaker intermolecular forces, leading to lower boiling points than straight-chain alkanes of comparable molecular weight.