Under conditions of acid catalysis, alkenes react with water to form alcohols. As in the case with hydrogen halides, the addition reaction in the formation of alcohols is also governed by Markovnikov's rule. An alkene of approximate molar mass of \(42 \mathrm{~g}\) reacts with water and sulfuric acid to produce a compound that reacts with acidic potassium dichromate solution to produce a ketone. Identify all the compounds in the preceding steps.

Alkenes are unsaturated hydrocarbons that contain at least one carbon-to-carbon double bond. When an alkene undergoes a reaction with water—a process known as hydration—the result is the formation of an alcohol. This type of chemical reaction is important in organic chemistry because it transforms relatively inert alkenes into more reactive alcohols.

During the hydration of an alkene, water (H₂O) molecules are added across the double bond. One hydrogen atom (H) from the water molecule attaches to one carbon of the double bond, and the hydroxyl group (OH) attaches to the other carbon. The specific outcome of this reaction depends on the structure of the initial alkene and is guided by Markovnikov's rule, which predicts the orientation of proton and hydroxyl group attachment.

For instance, in the case of the alkene mentioned in the exercise, propene (C₃H₆), water adds across the double bond, ultimately yielding an alcohol, 2-propanol. The '2-' designator indicates that the hydroxyl group is attached to the second carbon of the propene molecule, aligning with Markovnikov's rule that prefavors the more substituted carbon atom.

Acid-catalyzed hydration is a specific method of adding water across an alkene's double bond, where an acid acts as a catalyst to speed up the reaction. In this type of reaction, the alkene first reacts with the acid, leading to the formation of a carbocation intermediate. This positively charged intermediate is then attacked by water, which donates a lone pair of electrons to bond with the carbocation, forming an alcohol.

The function of the acid in this scenario is twofold: it helps in the generation of the carbocation by protonating the alkene, and it provides the acidic environment necessary for the reaction to proceed smoothly. Common acids used in acid-catalyzed hydrations include sulfuric acid (H₂SO₄) and phosphoric acid (H₃PO₄), both of which are strong enough to facilitate the creation of the carbocation without participating as a reactant in the final product.

In our exercise example, sulfuric acid catalyzes the hydration of propene to form 2-propanol. This is a critical step because, without the presence of a strong acid, the reaction rate would be significantly slower or the reaction might not occur at a noticeable rate at all.

Ketones are organic compounds characterized by a carbonyl group (C=O) bonded to two carbon atoms. They are an important class of compounds in organic chemistry due to their diverse applications and reactivity.

In the context of the given problem, the ketone forms through the oxidation of an alcohol. Oxidation in organic chemistry typically refers to an increase in the number of bonds from carbon atoms to more electronegative atoms (usually oxygen), often resulting in the formation of carbonyl groups. For primary and secondary alcohols, the process can yield aldehydes and ketones, respectively.

Secondary alcohols, like the formed 2-propanol, will oxidize to ketones when treated with strong oxidizing agents. The acidic potassium dichromate (K₂Cr₂O₇) solution mentioned in the exercise is one such agent, capable of efficiently transforming 2-propanol into propanone, commonly known as acetone. During this reaction, the secondary alcohol's hydroxyl group (OH) is replaced with a carbonyl group (C=O), converting it into the ketone. It's an essential reaction in organic synthesis, allowing chemists to easily manipulate molecules and create a variety of complex structures.

Understanding ketone formation through oxidation reactions is essential for students of organic chemistry as it underlies the synthesis and transformation of countless organic compounds.