The hydrogen-bonding capacity of an alcohol increases the boiling point and melting point relative to the analogous hydrocarbon. Thus, methanol has a higher boiling point and a higher melting point than methane.
Branching tends to decrease van der Waals' forces, thereby decreasing the boiling point. The boiling point of alcohols with identical molecular weights would be expected to increase in the order: 3o
(i.e. primary alcohols have a higher b.p)
- Alcohol molecules are polar; they possess a permanent molecular dipole moment.
- As a result, all alcohols are soluble in polar solvents. Solubility is decreased by increasing chain length and by branching, since both of these effects serve to lessen the dipole moment (and, thus, the
- polarity) of alcohol.