Problem 147 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following would, on ozonolysis, yields \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) and \(\mathrm{CH}_{2}(\mathrm{CHO})_{2}\) in the ratio \(1: 1\) ? (a) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\) (b) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\) (d) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{C}\left(\mathrm{CH}_{3}\right)=\mathrm{CH}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}-\) \(\mathrm{CH}_{3}\)

Step-by-Step Solution

Answer

Option (d) yields the required products upon ozonolysis.

Step 1: Understand Ozonolysis Products

Ozonolysis is a reaction where alkenes are cleaved by ozone to form carbonyl compounds. For this exercise, we need a compound that upon ozonolysis, produces acetone (\(\mathrm{CH}_3\mathrm{COCH}_3\)) and glyceraldehyde dimer (\(\mathrm{CH}_2(\mathrm{CHO})_2\)).

Step 2: Analyze Product Structures

Acetone is a simple ketone with the structure \(\mathrm{CH}_3\mathrm{C}(=\mathrm{O})\mathrm{CH}_3\), and the glyceraldehyde dimer, \(\mathrm{CH}_2(\mathrm{CHO})_2\), is two formaldehyde molecules linked by a carbon atom.

Step 3: Compare Each Option

Analyze each given compound to see if breaking the double bonds through ozonolysis leads to the required products: - **Option (a):** Contains no internal C=C db that aligns with acetone requirement. - **Option (b):** 1. Terminal dbs lead to incorrect products. - **Option (c):** 1. Yields different fragments not aligned desired products. - **Option (d):** 1. Middle db combine to give acetone and terminal db give glyceraldehyde.

Step 4: Verification of Option (d)

Option (d) with the structure \((\mathrm{CH}_3)_2\mathrm{C}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{C}(\mathrm{CH}_3)=\mathrm{CH}-\mathrm{CH}_2-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_3\) is a long chain with appropriate placements of double bonds that yield exactly one molecule of acetone and one dimer of the glyceraldehyde upon ozonolysis quite fitting the constructs needed.

Key Concepts

Alkene Reaction

Reactions involving alkenes are quite significant in organic chemistry due to the reactivity of the carbon-carbon double bond. An alkene is characterized by the presence of at least one double bond between carbon atoms. This double bond is highly reactive, making alkenes excellent candidates for various addition reactions. One key reaction involving alkenes is ozonolysis, where alkenes react with ozone, \((O_3)\), to cleave the double bonds and form different types of carbonyl compounds. Some important points about alkene reactions include:

• Alkenes are unsaturated hydrocarbons with a general formula of \(C_nH_{2n}.\)
• The double bond in alkenes makes them undergo electrophilic addition reactions.
• Ozonolysis is an oxidative cleavage reaction resulting in the formation of aldehydes, ketones, or both, depending on the alkene's structure.

Understanding the reactivity of alkenes and how they participate in reactions like ozonolysis is fundamental for JEE chemistry, as it forms the basis for synthesis and analysis in organic chemistry.

Carbonyl Compound Formation

Ozonolysis is particularly noteworthy for its ability to transform alkenes into carbonyl compounds. Carbonyl groups, denoted by the structure \((C=O),\) are pivotal in many organic reactions and are key structures in a wide variety of organic compounds. Upon ozonolysis, an alkene undergoes cleavage, and each carbon of the double bond ends up as part of a carbonyl group. For example, if we consider the ozonolysis of the compound corresponding to option (d) in the exercise, the double bonds split as follows:- The double bond near the center of the chain results in the formation of acetone, \((CH_3COCH_3).\)- The terminal double bond leads to the formation of the glyceraldehyde dimer, \((CH_2(CHO)_2),\) which is effectively two formaldehyde units.This step of identifying the position of double bonds and predicting the resulting carbonyl compounds is critical in solving problems around ozonolysis, especially in exams like the JEE.

JEE Chemistry Problem

Being prepared for JEE chemistry means comprehending and applying concepts of reaction mechanisms in problems like ozonolysis. This exercise demonstrates a typical problem where understanding structures and predicting reaction outcomes is vital. To succeed in such problems:

• Familiarize yourself with diverse organic reactions, particularly those involving alkenes.
• Practice identifying functional groups and predicting reaction outcomes.
• Understand structural isomerism and its impact on reaction products.
• Use the structural formula to spot potential carbonyl groups after ozonolysis.

In this specific problem, analyzing the structure and correctly identifying the required products of acetone and glyceraldehyde dimer leads you to option (d). Practicing these types of problems enhances problem-solving skills critical for excelling in JEE chemistry.