What intermolecular forces are present in alcohol?
There are basically 3 - dipole/dipole, London Dispersion, and H-Bonds. The length of the alcohol basically determines whether or not they associate with water.
Short chain alcohols have intermolecular forces that are dominated by H-bonds and dipole/dipole, so they dissolve in water readily (infinitely for methanol and ethanol). As the carbon chain gets longer, the contribution of the London dispersion forces becomes significant.
I think the cutoff is about 5 carbons - when you have n-pentanol, this molecule is sparingly soluble in water, even though it still has dipole/dipole and H-Bonds....the London Dispersion Forces contribute "more" and the molecule ends up not liking water.