Lecture #29
Sections from Chapters 12 and 13 (See Syllabus = in Main Index)
  CURMUDGEON GENERAL'S WARNING. These "slides" represent highlights from lecture and are neither complete nor meant to replace lecture. It is advised not to use these as a reliable means to replace missed lecture material. Do so at risk to healthy academic performance in 09-105.
  Intermolecular Interactions
  • Liquids and Solids

  • Hydrogen Bonding

  • Molecular Basis of Solubility
Boiling point effects owed to hydrogen bonding
Multiple hydrogen bonds
A comparison of melting points of two similar looking compounds, both are benzene rings with "hydroxy" and "nitro" substituents in different positions. For comparison, below on the left, the "hydroxy" group has been replaced by a "methyl" group.
Melting points are also affected by hydrogen bonding.
The melting points of these two structural isomers of nearly identical electronic volumes differ substantially. Why?
An illustration of an "intramolecular" hydrogen bond within a molecule (rather than between molecules).
Some definitions relevant to discussions on solubility.
What effects determine solubility?
The dependence of the solubilities of different alcohols on their molecular structure
Interpretation of alcohol solubilities in terms of molecular structure and intermolecular interactions
 Another comparison to make.  
Vitamin A shown here is essentially a nonpolar molecule. It is very polarizable because of its "size" (and also because pi electrons are very polarizable, a detail we haven't worried about and will not). Consequently, it is not very soluble in water but quite soluble in a nonpolar solvent such as "fat" (which is mostly hydrocarbon-like in nature).
In contrast to Vitamin A, you can see here from the structure of Vitamin C that extensive hydrogen bonding with solvent water molecules should be possible, explaining why it is a water soluble vitamin.
Acetic acid, as a small, polar molecule capable of hydrogen bonding with water is very soluble in water. You might reasonably expect it to be insolube in nonpolar solvents. However, a subtle phenomenon causes acetic acid to be soluble in nonpolar solvents as well. See below.
Acetic acid can effectively "dimerize", form a double structure held togeter very effectively by a geometrical arrangement that accommodates double hydrogen bonding. The resulting structure has no dipole moment. The "dimer" can then serve as a solvent in nonpolar solvents.