Question

In the following sequence of reactions, the alkene affords the compound ' \(\mathrm{B}\) ' \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{3} \stackrel{\mathrm{O}_{3}}{\longrightarrow}(\mathrm{A}) \stackrel{\mathrm{H}_{2} \mathrm{O}}{\mathrm{Zn}}\) The compound (B) is (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{CHO}\)

Short answer

(d) \(\mathrm{CH}_{3}\mathrm{CHO}\).

Step-by-step solution

Understand the Reaction

The reaction in question involves the conversion of an alkene using ozone. This is a typical ozonolysis reaction where the double bond of the alkene is cleaved to form carbonyl compounds.

Analyze the Given Alkene

The starting alkene is \(\text{CH}_3\text{CH=CHCH}_3\) (2-butene). It has a double bond between the second and third carbon atoms.

Ozonolysis Process

In the presence of ozone (\(\text{O}_3\)), the double bond in the alkene is cleaved. Ozone initially forms an ozonide intermediate, which is then cleaved to form the final products during workup with reducing agents like Zn and water.

Identify the Products of Ozonolysis

Ozonolysis of 2-butene breaks the double bond and forms two molecules of acetaldehyde \(\text{CH}_3\text{CHO}\). This is because each half of the alkene forms one mole of aldehyde, split at the double bond.

Choose the Correct Answer

From the multiple-choice options, the correct final product after ozonolysis and reduction is option (d) \(\text{CH}_3\text{CHO}\).

Key concepts

Alkene Reactions

Alkenes are hydrocarbons containing at least one carbon-carbon double bond. These double bonds make alkenes highly reactive and enable them to participate in various chemical reactions. One of the most common types of reactions involving alkenes is the addition reaction, where atoms are added across the double bond.
However, ozonolysis is a specific reaction involving alkenes. It is characterized by the cleavage of the carbon-carbon double bond followed by oxidation. Unlike simple additions, ozonolysis leads to the formation of carbonyl compounds. Understanding these reactions is crucial as they help in converting unsaturated compounds into simpler forms, influencing the production of several key chemicals.

Carbonyl Compounds

Carbonyl compounds are characterized by the presence of a carbonyl group, which consists of a carbon atom double-bonded to an oxygen atom (C=O). These compounds include aldehydes, ketones, acids, and esters.
In the context of ozonolysis, the cleavage of double-bond in alkenes results in carbonyl compounds such as aldehydes or ketones. The nature of carbonyl compounds produced depends on the structure of the starting alkene. For instance, if a terminal alkene is used, the reaction mainly results in aldehydes. On the other hand, internal alkenes often produce both aldehydes and ketones. Therefore, understanding the nature and reactivity of carbonyl compounds is essential in predicting and analyzing the outcomes of alkene ozonolysis.

2-butene Ozonolysis

2-butene is an example of a simple alkene, represented by the chemical formula \( ext{CH}_3 ext{CH=CHCH}_3\). When subjected to ozonolysis, the double bond in 2-butene interacts with ozone molecules, leading to its cleavage.
The reaction starts with the formation of an ozonide intermediate, which is then decomposed using reducing agents like zinc and water. This process results in two molecules of acetaldehyde (\( ext{CH}_3 ext{CHO}\)). The transformation of 2-butene into acetaldehyde showcases how straightforward ozonolysis of symmetrical alkenes can be, as both halves of the molecule yield the same product.

Cleavage of Double Bonds

The cleavage of double bonds is a key concept in understanding the reactivity of alkenes. This process is important in many chemical reactions, particularly ozonolysis. During ozonolysis, ozone attacks the double bond, forming a mixture that breaks down into smaller carbonyl compounds.
- *Formation of Intermediates:* The primary step involves the formation of an ozonide. - *Reduction Step:* This ozonide is then reduced, breaking the bond and resulting in the final carbonyl products. Through these transformations, ozonolysis provides a powerful method of splitting double bonds and thus significantly reconfiguring the structure of organic compounds. Understanding this process allows chemists to predict the types of products that can be obtained from different alkenes.