Question

\(\mathrm{Q} \rightarrow \mathrm{P}\) cannot be carried out by using (A) \(\mathrm{MnO}_{2}\) (B) \(\mathrm{PCC}\) (C) \(\mathrm{Cu} / 300^{\circ} \mathrm{C}\) (D) \(\mathrm{Al}\left(\mathrm{OCMe}_{3}\right)_{3}\) in Acetone

Short answer

The reagent that cannot be used to perform the \(Q \rightarrow P\) reaction is (D) \(Al(OCMe_{3})_{3}\) in Acetone, as it carries out reduction reactions rather than the required oxidation for the \(Q \rightarrow P\) reaction.

Step-by-step solution

Identifying Reactions Associated with Each Reagent

Now let's look at each reagent and its associated reactions: (A) \(MnO_{2}\) - Manganese dioxide: It is an oxidizing agent often used in selective oxidation of allylic alcohols to aldehydes or ketones. (B) \(PCC\) - Pyridinium Chlorochromate: It is a reagent for mild oxidation of primary and secondary alcohols to aldehydes and ketones, respectively. (C) \(Cu / 300^{\circ}C\) - Copper at 300 degrees Celsius: This reagent is often used in the dehydrogenation of alcohols, specifically, the conversion of primary alcohols to aldehydes and secondary alcohols to ketones. (D) \(Al(OCMe_{3})_{3}\) in Acetone (Aluminium Isopropoxide in Acetone): This reagent combination is used in the Meerwein–Ponndorf–Verley reduction, which reduces aldehydes or ketones to primary or secondary alcohols.

Determining the Answer

Based on our analysis of each reagent, we can conclude that the reagent that cannot be used to perform the \(Q \rightarrow P\) reaction is: (D) \(Al(OCMe_{3})_{3}\) in Acetone: Since it carries out reduction reactions rather than oxidation needed for the \(Q \rightarrow P\) reaction, this reagent is not suitable.

Key concepts

Oxidizing Agents

In organic chemistry, oxidizing agents are vital for transforming alcohols into more oxidized forms like aldehydes and ketones. These agents facilitate the removal of hydrogen or the addition of oxygen to a substrate.
Common oxidizing agents include oxygen, ozone, and various metal oxides like manganese dioxide (\(MnO_{2}\)). For instance, \(MnO_{2}\) is selectively used for oxidizing allylic alcohols to aldehydes or ketones. This means it targets specific types of functional groups and leaves others untouched, which can be valuable in complex synthetic sequences.
When choosing an oxidizing agent, several factors are considered:

• Selectivity: The ability to oxidize one functional group in preference to another.
• Strength: Which determines how much oxidation it can achieve.
• Compatibility: Whether it will react or interfere with other parts of the molecule.

By understanding oxidizing agents, chemists can effectively plan and control organic synthesis reactions to obtain the desired product.

Reduction Reactions

Reduction reactions are the opposite of oxidation reactions, focusing on the gain of hydrogen or the loss of oxygen. These processes are essential in converting more oxidized compounds back to their less oxidized forms.
For example, the Meerwein–Ponndorf–Verley reduction is a well-known reduction reaction. It involves using aluminum isopropoxide to reduce aldehydes and ketones back to alcohols.
Reduction reactions can be identified by:

• Product Formation: Generally, a reduction will produce an alcohol from an aldehyde or ketone.
• Use of Reducing Agents: Common reducing agents include lithium aluminum hydride (LiAlH4) and sodium borohydride (NaBH4).
• Reaction Conditions: Terms like "metal in acid" often imply reduction pathways.

Reduction reactions help synthesize many important organic compounds by manipulating the oxidation states of molecules.

Alcohol Conversions

Alcohol conversions are fundamental reactions where alcohols are transformed into other functional groups such as aldehydes, ketones, or esters. The choice of reagent and reaction conditions dictate the product of conversion.
For instance, using pyridinium chlorochromate (PCC), a primary alcohol can be oxidized to form an aldehyde, while a secondary alcohol will yield a ketone. This reagent is favored for its mildness, avoiding overoxidation to carboxylic acids.
Conversion pathways often involve:

• Oxidation: Where alcohols lose hydrogen atoms.
• Dehydration: Removing water to form alkenes.
• Substitution: Replacing the hydroxyl group with another group (like halides).

Understanding the nuanced pathways of alcohol conversions gives chemists precise control over obtaining desired end products from alcohol starting materials.

Aldehydes and Ketones

Aldehydes and ketones are key players in organic synthesis due to their versatile chemistry. These carbonyl-containing compounds serve as crucial intermediates in various synthetic schemes.
Aldehydes have a carbonyl group attached to at least one hydrogen, making them more reactive than ketones, which have carbon groups on both sides. This variation influences their reactivity and their role in synthetic routes.
Some typical reactions involving aldehydes and ketones include:

• Nucleophilic Addition: Because of the partial positive charge on the carbonyl carbon, aldehydes and ketones are prone to attack by nucleophiles.
• Redox Reactions: As discussed, they can be reduced to alcohols or oxidized under rare conditions to acids.
• Formation of Derivatives: Producing imines, hydrazones, or acetals used for further transformations.

By mastering aldehyde and ketone chemistry, chemists enhance their ability to design and execute efficient synthetic strategies.