Physical properties of organic molecules depend both on the nature of the functional group and the size and shape of the molecule. Organic chemists often use the water solubility or insolubility as a means of separating organic substances from one another or organic substances from inorganic substances that may be present in reaction mixtures.
How can water solubility be correlated with structure?
For a substance to be water-soluble
Organic molecules containing moderately polar or polar functional groups and fewer than five carbons are water-soluble because
Even if a polar functional group is present, the water solubility of organic compounds decreases as the number of carbons increases.
How can water solubility be correlated with structure?
For a substance to be water-soluble
the attractive forces between the particles of the substance with water must be at least as strong as
the attractive forces between the particles of the substance with itself and the attractive forces between water molecules.
Hydrocarbons are insoluble in water becausethe attractive forces between the particles of the substance with itself and the attractive forces between water molecules.
the water molecule-hydrocarbon molecule attractive forces are weaker than the hydrocarbon-hydrocarbon and water-water attractive forces
Organic molecules containing moderately polar or polar functional groups and fewer than five carbons are water-soluble because
the attractive forces between water and polar region of the organic molecule are stronger than for a hydrocarbon.
| CH3CH2CH3 | CH3CH2CH2Cl | CH3OCH3 | |
| water solubility | none | very low | soluble |
 | CH3CH2OH |  |
| soluble | soluble | soluble |
Even if a polar functional group is present, the water solubility of organic compounds decreases as the number of carbons increases.
(CH3OCH3 328 g L–1 CH3CH2OCH2CH3 8 g L–1)
Even carboxylic acids with greater than five carbons are water-insoluble.
Even carboxylic acids with greater than five carbons are water-insoluble.