Despite possessing a highly polar carbon-halogen bond (e.g., D for chloroethane), simple alkyl halid — Haloalkanes and Haloarenes Chemistry Question
Question
Despite possessing a highly polar carbon-halogen bond (e.g., $\mu \approx 2.05$ D for chloroethane), simple alkyl halides are practically completely immiscible and insoluble in water. Which thermodynamic argument most accurately explains this stark observation?
💡 Solution & Explanation
For a solute to dissolve, it must break the intermolecular forces within both the pure solute and the pure solvent, and form new solute-solvent interactions. Water molecules are bound by a pervasive, highly energetic network of hydrogen bonds. Alkyl halides cannot form hydrogen bonds with water. The weak dipole-dipole or dipole-induced dipole attractions formed between water and the alkyl halide release very little energy—far too little to compensate for the massive enthalpy required to break the water-water hydrogen bonds. Thus, dissolution is thermodynamically unfavorable.