Question

\(\mathrm{Ph}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{3} \stackrel{\mathrm{H}_{\mathrm{g}}^{+2} / \mathrm{H}^{+}}{\longrightarrow} \cdot\) A. Here, \(\mathrm{A}\) is: (a) CCC(=O)c1ccccc1 (b) CC(=O)Cc1ccccc1 (c) CCC(O)c1ccccc1 (d) CC(O)c1ccccc1

Short answer

The product A is option (a): CCC(=O)c1ccccc1.

Step-by-step solution

Identify the Reactant

The initial compound is propyne with a phenyl group at one end, represented as \( \text{Ph}-\text{C} \equiv \text{C}-\text{CH}_3 \), where \( \text{Ph} \) stands for a phenyl group (C6H5-). It is an alkyne.

Understand the Reaction Conditions

The reaction involves using \( \text{Hg}^{+2} / \text{H}^{+} \), known as mercuric ion-catalyzed hydration of an alkyne. This reaction typically converts the alkyne into a ketone.

Apply Markovnikov's Rule

The hydration of the alkyne follows Markovnikov's rule, meaning the hydrogen from water adds to the carbon with more hydrogen atoms initially, and the OH group adds to the other carbon. In this case, PT followed by conversion to the ketone.

Determine the Ketone Structure

Upon hydration, the tautomerization of the initial enol (from the addition of water) results in a ketone. The carbon adjacent to the phenyl group becomes the carbonyl group.

Draw the Product

The resulting product from hydration of \( \text{Ph}-\text{C} \equiv \text{C}-\text{CH}_3 \) is an aromatic ketone. Specifically, the structure corresponds to: \( \text{CCC}(=\text{O})\text{c}1\text{ccccc}1 \), which matches option (a).

Key concepts

Alkyne Hydrolysis

Alkyne hydrolysis is a fascinating reaction in organic chemistry. It involves the addition of water molecules across a carbon-carbon triple bond, specifically within alkynes. Under certain conditions, such as the presence of mercuric ions ( Hg^{+2} ) and an acidic environment ( H^{+} ), alkynes undergo a transformation. This process involves breaking the strong triple bond between the carbon atoms and forming new bonds with the elements of water: hydrogen (H) and hydroxyl group (OH).

• Initially, the terminal alkyne reacts in the presence of the catalyst to form an unstable enol.
• The enol generated is in equilibrium with a more stable ketone form, which we'll delve into later.

This reaction is a practical example of how chemistry can elegantly convert a simple hydrocarbon into a more complex carbonyl compound, often increasing its reactivity and usefulness in further reactions.

Markovnikov's Rule

Markovnikov's Rule is key in predicting the outcome of addition reactions involving water or hydrogen halides to alkynes and alkenes. Named after Russian chemist Vladimir Markovnikov, the rule provides a simple yet brilliantly effective guideline: during reactions, the hydrogen atom tends to bind to the carbon with more hydrogen atoms already attached, while the other component (like an OH group) attaches to the other carbon.

• In the context of alkyne hydrolysis, this rule predicts how the elements of water will add to the alkyne skeleton.
• The hydrogen ion attaches to the carbon that begins with more hydrogen atoms, and the OH group attaches to the less substituted carbon.

This heuristic not only helps in predicting the products of many reactions but serves as an essential tool for understanding reaction mechanisms in organic chemistry.

By following Markovnikov's Rule, chemists can consistently foresee the structure of the hydrolysis product, making it easier to plan synthetic routes and understand how molecular transformations occur.

Tautomerization

Tautomerization is a fascinating concept that introduces dynamics into the usually static world of molecule structures. It refers to the process through which a molecule like an enol isotype shifts to a more stable ketone or aldehyde form, or vice versa. This equilibrium between the two forms is chemically reversible and occurs due to the relocation of a hydrogen atom and the shifts in some double bonds.

• In the hydrolysis of an alkyne, once the enol form is produced, it almost spontaneously rearranges itself to convert into a keto form.
• Ketones are generally more stable, which is why the tautomerization from an enol to ketone is a preferred and common outcome.

Understanding tautomerization is crucial because it not only affects the stability of molecules but also influences their reactivity and behavior in subsequent reactions. Moreover, tautomerization exemplifies the delicate interplay of forces within molecules, showcasing the beautiful yet intricate dance of atoms involved in organic transformations.