Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

The products formed by the ozonolysis-hydrolysis of a compound of formula, \(\mathrm{C}_{5} \mathrm{H}_{8}\) are \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}\) and \(\mathrm{CO}_{2}\). The compound is (a) pent-2-yne (b) pent-1-yne (c) penta-1, 3 -diene (d) penta-1, 4 -diene

Step-by-Step Solution

Answer

The compound is (b) pent-1-yne.

Step 1: Understanding Ozonolysis

Ozonolysis is a reaction where ozone breaks multiple bonds in alkenes and alkynes. In alkynes, ozonolysis can lead to oxidative cleavage, resulting in carboxylic acids or carbon dioxide if terminal alkynes are present.

Step 2: Review Given Products

The problem states that the products of the ozonolysis and hydrolysis of a compound with formula \( \mathrm{C}_5 \mathrm{H}_8 \) are \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH} \) and \( \mathrm{CO}_2 \). These are a carboxylic acid and carbon dioxide, respectively.

Step 3: Analyzing Possible Compounds

The given compounds are potential structures of \( \mathrm{C}_5 \mathrm{H}_8 \): (a) pent-2-yne, (b) pent-1-yne, (c) penta-1,3-diene, and (d) penta-1,4-diene. We will analyze which can produce the given products by ozonolysis.

Step 4: Evaluate Option (b) Pent-1-yne

Pent-1-yne is an alkyne with the structure \( \mathrm{CH}_3 - \mathrm{CH}_2 - \mathrm{C} \equiv \mathrm{C} - \mathrm{H} \). Terminal alkynes, like pent-1-yne, can produce a carboxylic acid and \( \mathrm{CO}_2 \). By ozonolysis, the alkyne bond is cleaved to form \( \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{COOH} \) from the internal portion and \( \mathrm{CO}_2 \) from the terminal carbon.

Key Concepts

Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond, denoted by the suffix -yne in their name. The simplest alkyne is ethyne (or acetylene), with the formula \( ext{C}_2 ext{H}_2 \). Alkynes are more reactive than alkanes due to the electron-rich triple bond, making them susceptible to a variety of reactions, including ozonolysis.

Ozonolysis involves the reaction of ozone \( (O_3) \) with the triple bond of an alkyne. This reaction cleaves the bond, leading to the formation of carbonyl-containing products.

• For internal alkynes, such as pent-2-yne, ozonolysis typically yields carboxylic acids.
• In terminal alkynes, like pent-1-yne, ozonolysis can produce a carboxylic acid and carbon dioxide or separate aldehyde fragments.

The reaction is particularly useful for identifying and characterizing alkynes, due to the specific breakdown patterns exhibited by different compounds.

Understanding the nature of the triple bond in alkynes helps predict the outcome of ozonolysis, which is often employed in organic synthesis and structural analysis.

Hydrolysis

Hydrolysis is a chemical process involving the splitting of bonds by the addition of water. In the context of organic chemistry, hydrolysis can convert semifinished compounds into more recognizable products, such as alcohols and carboxylic acids.

During ozonolysis of alkynes, hydrolysis plays a crucial role in transforming the immediate ozonide products to more stable compounds. Here's how it works:

• The initial ozonide is formed when the alkyne reacts with ozone, creating an unstable intermediate.
• This intermediate then undergoes hydrolysis, breaking it down further into simpler compounds.

Critical to the process, hydrolysis ensures that the reactive paraphernalia formed during ozonolysis is effectively transformed into end products like carboxylic acids or other oxidized carbon fragments. Understanding hydrolysis can enlighten students on how complex reactions can be steered toward generating familiar organic products.

Carboxylic Acids

Carboxylic acids are a class of organic compounds characterized by the presence of a carboxyl group \((\text{-COOH})\). These acids are noted for their acidic properties, owing to the hydrogen in the carboxyl group that can be released as a proton.

They are typically formed in the ozonolysis and hydrolysis of alkynes and are significant in various biochemical cycles. For instance, during ozonolysis of a terminal alkyne like pent-1-yne, the process generates \( \text{CH}_3\text{CH}_2\text{CH}_2\text{COOH} \) via a specific conversion pathway.

• The exchange from an alkyne to carboxylic acid exemplifies how complex organic reactions can be controlled to yield straightforward products.
• This conversion contributes to understanding the structural breakdown of hydrocarbons and their use in synthesis.

Carboxylic acids serve as a fundamental topic in organic chemistry, underpinning many synthetic applications and practical implications.