Problem 187 - A Complete Resource Book in Chemistry for JEE Main

Question

On vigorous oxidation by permanganate solution, \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{CHO}\) gives (a) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\) and \(\mathrm{OHCCH}_{2} \mathrm{CHO}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}-\mathrm{CHCH}_{2} \mathrm{CHO}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\) and \(\mathrm{OHCCH}_{2} \mathrm{COOH}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CO}\) and \(\mathrm{CH}_{3} \mathrm{COO}^{\circ} \mathrm{H}\)

Step-by-Step Solution

Answer

The correct answer is (c) \((\mathrm{CH}_{3})_{2} \mathrm{CO}\) and \(\mathrm{OHCCH}_{2} \mathrm{COOH}\).

Step 1: Understanding the oxidation

When vigorous oxidation occurs with potassium permanganate, it typically cleaves carbon-carbon double bonds and oxidizes the resulting fragments to carboxylic acids or ketones if possible.

Step 2: Identifying the double bond

In the compound \( (\mathrm{CH}_{3})_{2} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{CHO} \), the double bond \( (\mathrm{C}=\mathrm{CHCH}_{2}) \) is the site of oxidation which breaks the molecule into two different parts.

Step 3: Analyzing the resulting fragments

Upon cleavage at the double bond, we get two fragments: an \( (\mathrm{CH}_{3})_{2} \mathrm{C} \) fragment and the rest of the molecule starting from \( \mathrm{CHCH}_{2} \mathrm{CHO} \).

Step 4: Oxidizing the fragments

The \( (\mathrm{CH}_{3})_{2} \mathrm{C} \) fragment is further oxidized into acetone \((\mathrm{CH}_{3})_{2} \mathrm{CO}\). The remaining fragment \( \mathrm{CHCH}_{2} \mathrm{CHO} \) is oxidized to \( \mathrm{OHCCH}_{2} \mathrm{COOH} \) due to the formation of a carboxylic acid.

Step 5: Choosing the correct answer

The oxidation of the initial compound gives acetone \((\mathrm{CH}_{3})_{2} \mathrm{CO}\) and \( \mathrm{OHCCH}_{2} \mathrm{COOH} \), which matches option (c).

Key Concepts

Oxidation Reactions

Oxidation reactions in organic chemistry typically involve the increase in the oxidation state of a molecule. This often includes the addition of oxygen or the removal of hydrogen from the molecular structure. In oxidation reactions, organic compounds like alcohols, aldehydes, and ketones can transform into carboxylic acids.
Common oxidizing agents include potassium permanganate (KMnO₄), which is particularly strong and often used under vigorous conditions to fully oxidize compounds.

Key points to remember about oxidation reactions:

• The oxidation state of carbon increases, often leading to the production of bonds with more electronegative atoms, such as oxygen.
• Oxidation can result in the cleavage of existing C-C double bonds, which is why it's such a critical process in organic transformations.
• Oxidation reactions are part of redox processes, meaning they always have a corresponding reduction reaction.

This knowledge forms the foundation for understanding more specific reactions, like permanganate oxidation.

Permanganate Oxidation

Permanganate oxidation uses potassium permanganate, a purple-colored compound, that acts as a strong oxidizer in organic reactions. It is widely applied to transform compounds with carbon-carbon double bonds into alcohols, ketones, or carboxylic acids.

Reaction details and applications include:

• When it reacts with alkenes (molecules with C=C bonds), KMnO₄ tends to break these bonds, converting them into carbonyl groups (C=O).
• The reaction is powerful enough to completely oxidize some organic fragments into carboxylic acids, making it an ideal choice for obtaining high oxidation state products.
• In solution, the presence of a hydroxide ion (OH⁻) ensures the permanganate ion remains effective, making sure that even terminal alkenes are fully oxidized to carboxylic acids rather than stopping at aldehydes.

The versatility of permanganate oxidation makes it valuable for organic synthesis, particularly in the study and breakdown of complex molecules.

Carbon-Carbon Double Bond Cleavage

Cleavage of carbon-carbon double bonds is a hallmark of oxidative reactions using strong oxidizers like potassium permanganate. The double bond is a concentrated area of electron density, making it reactive with oxidizing agents.

The cleavage typically involves:

• The breaking of the double bond into two separate organic fragments, each carrying parts of the original molecule.
• Subsequent oxidation of these fragments into compounds such as ketones or acids; in our example case, the cleavage gave rise to acetone and a carboxylic acid from the starting alkene.
• This property of cleaving and oxidizing provides a method not only for analyzing unknown compounds but also for modifying known compounds to create new substances with valuable characteristics.

Understanding double bond cleavage is crucial for chemists, as it impacts the fundamental design of reactions and the expected transformations of organic materials.