Nucleosides are stable in water and in dilute base. In dilute acid, however, the glycosidic bond of a nucleoside undergoes hydrolysis to give a pentose and a heterocyclic aromatic amine base. Propose a mechanism for this acid- catalyzed hydrolysis.

A nucleoside is an organic molecule that consists of a nitrogenous base (a heterocyclic aromatic amine) and a pentose sugar linked by a glycosidic bond. The glycosidic bond is formed between the 1'-position of the sugar and the base's nitrogen. In this exercise, the focus is on the hydrolysis of this bond in an acid-catalyzed reaction.

Hydrolysis is a chemical process where a molecule undergoes cleavage due to the addition of a molecule of water. In the case of a nucleoside, the reaction breaks the glycosidic bond, resulting in the formation of a pentose sugar and a heterocyclic aromatic amine base.

An acid-catalyzed reaction is a chemical reaction in which an acid acts as a catalyst to increase the rate of reaction. In this case, the acid will act as a proton donor, facilitating the breaking of the glycosidic bond in the nucleoside.

To propose the mechanism for the acid-catalyzed hydrolysis of a nucleoside, follow the steps below: 1. Protonation of the glycosidic oxygen: The acid donates a proton (H+) to the glycosidic oxygen atom in the nucleoside. This protonation results in the formation of a positively charged oxonium ion, making the glycosidic bond more susceptible to cleavage. \[\ce{Nucreloside + H+ <=> [Nucreloside-{H+}]^+}\] 2. Nucleophilic attack: A water molecule acts as a nucleophile and attacks the now positively charged glycosidic carbon. This will result in the formation of a pentavalent intermediate. \[\ce{[Nucreloside-{H+}]^+ + H2O <=> [Nucreloside-{(OH)2}-Intermediate]}\] 3. Cleavage of glycosidic bond: In this step, the glycosidic bond breaks, and the pentose sugar and heterocyclic aromatic amine base are formed. \[\ce{[Nucreloside-{(OH)2}-Intermediate] <=> Base + Sugar- {OH}}\] 4. Deprotonation of sugar: The sugar molecule acquires a proton (H+) from the surrounding solution, thus forming a neutral sugar molecule. The protonated base is formed as an intermediate species. \[\ce{Base + Sugar- {OH} <=> Base-{H+} + Sugar}\] 5. Deprotonation of base: The protonated base accepts a water molecule and returns to its original neutral state, regenerating the acid catalyst. \[\ce{Base-{H+} + H2O <=> Base + H3O+}\] In conclusion, the proposed mechanism involves the protonation of the glycosidic oxygen, nucleophilic attack by a water molecule, cleavage of the glycosidic bond, and the deprotonation of the sugar and base to form the final products. The whole balanced equation of the hydrolysis reaction is: \[\ce{Nucleoside + H2O <=> Base + Sugar + H3O+}\]