branched-chain isomers
Because isomers are different compounds, they have different properties. Generally, branched-chain isomers have lower boiling and melting points than straight-chain isomers. For example, the boiling and melting points of iso -butane are -12 C and -160 C, respectively, compared with 0 C and -138 C for n -butane. The more branching there is, the lower the boiling and melting points are.