The boiling points of butane and 2-methylpropane are both -0.5 °C. This is because both compounds have similar molecular weights and structures. Butane has a molecular weight of 58.12 g/mol, while 2-methylpropane has a molecular weight of 58.12 g/mol. Both compounds are also nonpolar, which means that they do not have any permanent dipole moments. This makes them both relatively weak intermolecular forces, which leads to low boiling points.