Bigger LDF vs Smaller Dipole-dipole: which takes precedence? [ENDORSED]

[Angel Shen 1E]

I’m curious why the textbook states that CHI₃ has a higher melting point than CHF₃. I thought that both of these molecules experience dipole-dipole interactions, so CHF₃ would have the higher melting point due to its larger dipole (greater electronegativity difference). Instead, CHI₃ has the higher melting point, suggesting that London dispersion forces are taking precedence. Why wouldn’t CHF₃’s dipole result in a higher melting point compared to CHI₃?

[Chem_Mod]

The dipole moment of C−Cl bond (1.86 Debye) in CH3−Cl is greater than dipole moment of C−F bond (1.85 Debye) in CH3−F.

Dipole moment = q x d

You are omitting the longer bond length for C-I contributing to the magnitude of the dipole.