text: As a hard base, water reacts readily with organic carbocations; for example in a hydration reaction, a hydroxyl group () and an acidic proton are added to the two carbon atoms bonded together in the carbon-carbon double bond, resulting in an alcohol. When the addition of water to an organic molecule cleaves the molecule in two, hydrolysis is said to occur. Notable examples of hydrolysis are the saponification of fats and the digestion of proteins and polysaccharides. Water can also be a leaving group in S2 substitution and E2 elimination reactions; the latter is then known as a dehydration reaction.