this is due only to the dispersion forces between the molecules, those dispersion forces must be strong. I have actually chosen these particular examples because they are non-polar, the delocalised electrons make them very polarisable to give temporary dipoles, and the molecules are flat so that they can lie closely together. The polarisability and the fact that the molecules can lie closely together help to make the dispersion forces strong. But it isn't very difficult to find examples of non-polar molecular compounds with fairly high boiling points, and therefore strong dispersion forces. A more familiar example comes from the fractional distillation of crude oil. Crude oil is a mixture of hydrocarbons of all sizes and shapes. These are non-polar molecules which would be held in the liquid by dispersion forces, and they range from gases to liquids with boiling points over 400C. There will be a wide range of strengths of the dispersion forces, from the relatively weak in gases like methane to the relatively strong in the sort of hydrocarbons which end up in products like bitumen. Both molecules have identical numbers of electrons, and the size of the two molecules is much the same. That means that you might expect the dispersion forces in both molecules to be similar (but see below). Fluorine is the most electronegative element, and therefore the carbon-fluorine bond is going to be very polar. However, even given the large permanent polarity of the molecule, the boiling point has only been increased by 10.2