Ammonia molecules are held together by hydrogen bonds. Ammonia behaves as if it had a higher molecular weight. Only the weaker London dispersion forces hold the CF 2 Cl 2 molecules together. Consider the boiling points of carbon dioxide and sulfur dioxide. What accounts for the huge difference in boiling point.
Molecular weight accounts for part of the difference.
But carbon dioxide is linear, sulfur dioxide is bent. The bent SO 2 has a dipole and the dipole-dipole interaction increases the intermolecular forces and raises its boiling point. Initially, there was concern about the toxicity of fluorocarbons based on earlier experiences of other researchers. This proved to be a false concern related to toxic impurities present in early samples. For these many reasons, CFC-12 quickly became the refrigerant of choice for most applications.