Solutions and Solubility

Like dissolves Like
When one substance dissolves in another, the intermolecular bonds in the solute must break, as must those in the solvent. The breaking of these bonds requires energy (endothermic) while the formation of new bonds between solvent and solute molecules releases energy. (exothermic)

If the strength of the bonds broken is too much greater than of those formed the substance will not dissolve.

Examples

1.
When NaCl dissolves in water the H-bonds between the water molecules break as do the ionic bonds between Na+ and Cl- ions. However the ion-dipole bonds that form between the H2O and the ions are very strong and so release much energy upn formation. This release of energy is close enough to the energy needed to break the initial bonds in the substances that the reaction can occur.

If NaCl was mixed with oil, the bonds between oil and ions would be ion-induced dipole, far too weak relative to the ionic bonding of NaCl to allow it to dissolve.

2.
When octanol is mixed with water it does not dissolve.
The dispersion forces between octanol molecules and the strong H-bonds of water must be overcome, however the bonds formed between water and octanol would only be dipole-induced dipole, too weak to offset the energy requirement for breaking the H-bonds.
If dissolved in oil however, only the disperion forces between oil molecules and those between octanol molecules would have to be overcome. The dispersion forces forming the bonds between solvent and solute would be enough that the energy released in these bonds formation would allow the reaction to occur.

(oil = any long chain length, non-polar molecule)

Extras
We can add the heats of the individual reactions together to get the overall heat of reaction thanks to Hess's Law.
If the overall reaction is exothermic, then when the solute dissolves heat will be released. This is
used in hot packs and self heating soups.
If it is endothermic it can still occur, as long as the enthalpy change is balanced by the entropy change. Such endothermic reactions are used in cold packs.