Problem 88 - A Complete Resource Book in Chemistry for JEE Main

Question

Identify the products of the following reaction, \(\mathrm{CH}_{3} \mathrm{C} \equiv \mathrm{CCH}_{2} \mathrm{CH}_{3} \frac{\text { (i) } \mathrm{O}_{3}}{\text { (ii) hydrolysis }} ?+?\) (a) \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CO}_{2}\) (b) \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{HOOC} \cdot \mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CHO}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\) (d) \(\mathrm{CH}_{3} \mathrm{COOH}+\mathrm{CH}_{3} \mathrm{COCH}_{3}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{CH}_{3} \mathrm{COOH} + \mathrm{HOOC} \cdot \mathrm{CH}_{2} \mathrm{CH}_{3}\) are the products.

Step 1: Understand the Reaction Type

The reaction involves an alkyne, \(\mathrm{CH}_{3} \mathrm{C}\equiv \mathrm{CCH}_{2} \mathrm{CH}_{3}\), undergoing ozonolysis followed by hydrolysis. In such reactions, the triple bond is cleaved and converted into two carbonyl groups.

Step 2: Draw the Structures

Draw the structure of the alkyne: \(\mathrm{CH}_{3} \mathrm{C}\equiv \mathrm{CCH}_{2} \mathrm{CH}_{3}\) is a carbon chain with a triple bond between the second and third carbon atoms. This molecule has five carbons in total.

Step 3: Predict the Cleavage

During ozonolysis of alkynes, each carbon involved in the triple bond becomes a carbonyl group. Specifically, the alkyne cleaves into two parts where one side produces carboxylic acid and the other a ketone or another carboxylic acid.

Step 4: Apply Ozonolysis Products

Ozonolysis will cleave the triple bond into two parts, each turning into a carboxylic acid. The triple bond between \(\mathrm{C}_2\) and \(\mathrm{C}_3\) in the alkyne structure divides the molecule into \(\mathrm{CH}_{3}\mathrm{COOH}\) and \(\mathrm{HOOC}\cdot\mathrm{CH}_2\mathrm{CH}_3\).

Step 5: Choose Correct Option

The products formed are \(\mathrm{CH}_{3}\mathrm{COOH}\) (acetic acid) and \(\mathrm{HOOC} \cdot \mathrm{CH}_2\mathrm{CH}_3\) (propanoic acid). Therefore, the correct answer is option (b).

Key Concepts

Alkyne Reactions

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond in their structure. This triple bond is a significant feature because it imparts unique reactivity to the molecule. When alkynes undergo reactions, the triple bond is often the target because of its high energy and its tendency to be converted into more stable forms. In ozonolysis, a powerful oxidizing agent called ozone (O_3) is used to break down alkynes. The triple bond is cleaved, and in its place, new functional groups are usually formed.

Ozonolysis of alkynes typically results in the formation of carbonyl-containing compounds. More specifically, each carbon atom originally involved in the triple bond can transform into a carboxylic acid if the ozonolysis is followed by hydrolysis. This transformation is a hallmark of the reactivity pattern of alkynes in the presence of strong oxidizing conditions.

Carboxylic Acid Formation

Carboxylic acids are organic compounds characterized by having a carboxyl group (COOH). In organic chemistry, carboxylic acids can be formed through various reactions, but a common method involves the oxidative cleavage of carbon-carbon multiple bonds, such as the triple bonds in alkynes.

When an alkyne undergoes ozonolysis, each carbon atom that made up the triple bond is converted into a carbonyl group, which upon hydrolysis can form a carboxyl group. For instance, when the molecule CH_3CCCH_2CH_3 is treated with ozone followed by water, each fragment of the former triple bond contributes to the creation of a carboxylic acid component. The resulting products, acetic acid (CH_3COOH) and propanoic acid (HOOCCH_2CH_3), exemplify this transformation pathway.

Organic Reaction Mechanisms

Organic reaction mechanisms are crucial for understanding how reactions proceed on a molecular level. They provide a detailed step-by-step description of how bonds are broken and formed in a chemical reaction. In the context of alkynes undergoing ozonolysis, the mechanism reflects the oxidative cleavage of the triple bond.

Initially, ozone reacts with the triple bond, forming an unstable intermediate called an ozonide. This intermediate allows the triple bond between the carbon atoms to break down. Subsequent hydrolysis, typically with water, results in the transformation of the intermediate into more stable carbonyl compounds, such as carboxylic acids. By understanding this mechanism, one can predict the types of products an alkyne will yield when subjected to similar conditions. This knowledge is invaluable for designing reactions and interpreting data from organic chemistry experiments.