The boiling point of a compound is determined by the strength of the intermolecular forces between its molecules. The stronger the intermolecular forces, the higher the boiling point.

The intermolecular forces between molecules can be dipole-dipole interactions, hydrogen bonding, or van der Waals forces.

Dipole-dipole interactions occur between molecules with permanent dipole moments. Hydrogen bonding is a special type of dipole-dipole interaction that occurs between molecules with a hydrogen atom bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine). Van der Waals forces are weak attractive forces that occur between all molecules.

The boiling point of a compound increases as the number of intermolecular forces between its molecules increases.

2,2-dimethylpropane has the highest boiling point of all the derivatives of ethane because it has the most intermolecular forces. 2,2-dimethylpropane is a nonpolar molecule, so it does not have any dipole-dipole interactions or hydrogen bonding. However, it does have strong van der Waals forces because it is a large molecule with a lot of surface area.

The other derivatives of ethane have fewer intermolecular forces than 2,2-dimethylpropane. For example, ethane is a nonpolar molecule, so it only has van der Waals forces. Butane is also a nonpolar molecule, but it has a higher boiling point than ethane because it is a larger molecule with more surface area. Propene is a polar molecule, so it has dipole-dipole interactions in addition to van der Waals forces. However, propene has a lower boiling point than 2,2-dimethylpropane because it is a smaller molecule with less surface area.

Therefore, 2,2-dimethylpropane has the highest boiling point of all the derivatives of ethane because it has the most intermolecular forces.