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Why do aldehydes with more than about five carbon atoms become poorly soluble in water?
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aldehyde
Alcohols may be oxidized to give aldehydes, ketones, and carboxylic acids. The oxidation of organic compounds generally increases the number of bonds from carbon to oxygen, and it may decrease the number of bonds to hydrogen.
The solubility of aldehydes in water is determined by the balance between their polar and nonpolar components.
Low-molecular-weight aldehydes are soluble in water because the oxygen atom of their carbonyl group can form hydrogen bonds with water molecules. However, as the length of the carbon chain increases beyond approximately five carbon atoms, the molecule's nonpolar hydrocarbon portion becomes increasingly dominant.
Because hydrocarbons are nonpolar and hydrophobic ("water-hating"), they cannot interact effectively with polar water molecules. Once the hydrocarbon chain is sufficiently long, this hydrophobic effect overrides the solubilizing influence of the polar carbonyl group, rendering the aldehyde poorly soluble in water.1