When comparing the boiling points of organic compounds, the general rule is that molecules with more carbon atoms tend to have higher boiling points. However, branching in a molecule can affect its boiling point.
In the case of dimethyl propane and butane, both compounds have the same number of carbon atoms, which is four. However, the arrangement of these atoms differs. Dimethyl propane (also known as 2,2-dimethylpropane) has a branched structure, while butane has a linear structure.
Branching in a molecule generally reduces the boiling point because it disrupts intermolecular forces, making it easier for the molecules to escape the liquid phase and enter the gas phase. In contrast, linear molecules can pack more closely together, resulting in stronger intermolecular forces and a higher boiling point.
Therefore, butane, with its linear structure, has a higher boiling point than dimethyl propane.