Question

Match the following columns: Column - I Column - II (Reaction) (Type of reactions) (A) \(\mathrm{R}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{CrO}_{3}}{\longrightarrow}\) (P) Dehydrogenation (Q) 4 mole of oxidising agent required for 6 mole of reactant to complete oxidation (C) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{MnO}_{2}}{\longrightarrow}\) (R) Dehydration (D) (S) Elimination reaction

Short answer

The correct matching for the given reactions is: (A) Dehydrogenation (C) Dehydration

Step-by-step solution

Identify Reaction (A)

First, let's look at reaction (A): \(\mathrm{R}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{CrO}_{3}}{\longrightarrow}\) In reaction (A), a primary alcohol \(\mathrm{R}-\mathrm{CH}_{2}-\mathrm{OH}\) is oxidized by \(\mathrm{CrO}_{3}\) (chromium trioxide), which is a strong oxidizing agent. The primary alcohol loses hydrogen, causing a dehydrogenation reaction. So, we match (A) with (P).

Identify Reaction (C)

Now, let's look at reaction (C): \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{OH} \stackrel{\mathrm{MnO}_{2}}{\longrightarrow}\) In reaction (C), an allylic alcohol (which has an -OH group adjacent to a carbon-carbon double bond) undergoes oxidation using \(\mathrm{MnO}_{2}\) (Manganese dioxide) as an oxidizing agent. This process involves the elimination of a water molecule (\(\mathrm{H}_{2}\mathrm{O}\), from the -OH group and an adjacent hydrogen) and forms a double bond, known as a dehydration reaction. So, we match (C) with (R).

Final Matching

Based on our analysis, the correct matching is: (A) with (P): Dehydrogenation (C) with (R): Dehydration

Key concepts

Dehydrogenation

Dehydrogenation is a chemical reaction that involves the removal of hydrogen from a molecule. This process is crucial in organic chemistry, particularly in the transformation of alcohols to other types of compounds. When a primary alcohol undergoes dehydrogenation, it loses hydrogen atoms, resulting in the formation of an aldehyde or ketone. This type of reaction is often facilitated by strong oxidizing agents, such as chromium trioxide ( CrO_3 ). Understanding dehydrogenation is important as it plays a role in synthesizing various organic compounds, which are essential in pharmaceuticals and industrial chemistry applications.

Dehydration

Dehydration reactions in organic chemistry refer to the removal of water (H₂O) from a molecule. These reactions are significant in transforming alcohols into alkenes. During dehydration, an alcohol loses a hydroxyl group (OH) and a hydrogen atom from an adjacent carbon, resulting in the formation of a new double bond between the carbons. This transformation changes the molecular structure significantly, often leading to entirely different chemical properties. An example of a dehydration reaction is seen when allylic alcohol undergoes treatment with an oxidizing agent, such as manganese dioxide ( MnO_2 ), leading to the elimination of water and forming a carbon-carbon double bond.

Oxidation reactions

Oxidation reactions are a class of chemical reactions where electrons are transferred from one substance to another. In organic chemistry, this often involves either adding oxygen or removing hydrogen from a molecule. For alcohols, oxidation typically results in the conversion of primary alcohols to aldehydes and subsequently to carboxylic acids with further oxidation. The use of oxidizing agents like chromium trioxide ( CrO_3 ) or manganese dioxide ( MnO_2 ) facilitates these transformations by removing hydrogen atoms and enabling new bonds to form. Recognizing these reactions is key to predicting and understanding the behavior of different organic compounds in chemical synthesis.

Primary alcohol

Primary alcohols are a type of alcohol where the hydroxyl (-OH) group is attached to a carbon atom that is only connected to one other carbon atom. This makes them particularly reactive and prone to oxidation. In reactions, primary alcohols often transform into aldehydes and can further oxidize to form carboxylic acids. The reactivity of primary alcohols makes them valuable in synthetic chemistry, where precise and controlled modification of molecular structures is required. Recognizing a compound as a primary alcohol helps predict its behavior in various chemical reactions, such as oxidation and dehydrogenation, leading to effective use in practical applications.

Allylic alcohol

An allylic alcohol is characterized by having a hydroxyl group (-OH) situated on a carbon atom adjacent to a carbon-carbon double bond. This unique positioning makes allylic alcohols especially reactive in chemical processes, such as oxidation and dehydration. In the presence of certain oxidizing agents, such as manganese dioxide ( MnO_2 ), allylic alcohols can undergo oxidation, resulting in the removal of water and formation of new double bonds. This characteristic makes them crucial intermediates in the synthesis of complex organic molecules. Understanding the behavior of allylic alcohols can significantly influence the design and outcome of organic synthesis strategies.