Question

Reductive ozonolysis of the alkene, \(\mathrm{CH}_{3}-\mathrm{CH}=\mathrm{C}=\mathrm{CH}_{2}\) will give: (a) Only \(\mathrm{CO}_{2}\) (b) Only \(\mathrm{CH}_{2}^{2} \mathrm{O}\) (c) Only \(\mathrm{CH}_{3}^{2}-\mathrm{CHO}\) (d) Mixture of \(\mathrm{CH}_{3} \mathrm{CHO}, \mathrm{HCHO}\) and \(\mathrm{CO}_{2}\)

Short answer

Option (d): Mixture of CH_3CHO, HCHO and CO_2.

Step-by-step solution

Understand the Reaction

Ozonolysis is a reaction where ozone (O_3) breaks the double bonds in alkenes. In reductive ozonolysis, this process is followed by reduction, typically using Zn/H_2O (zinc in water), which converts the ozonolysis products to carbonyl compounds, such as aldehydes or ketones, instead of carboxylic acids.

Analyze the Alkene Structure

Observe the given alkene, CH_3-CH=C=CH_2. It has a double bond between the second and third carbon atoms. This unique structure will dictate how the ozonolysis breaks the molecule.

Break the Double Bond

In ozonolysis, each double bond in the alkene breaks, and oxygen atoms are introduced. For the given alkene, breaking each double bond will initially form ozonides, which will be further broken down upon reduction to carbonyl compounds.

Determine the Products

When the double bonds in CH_3-CH=C=CH_2 are broken, the expected products initially are formaldehyde (HCHO), acetaldehyde (CH_3CHO), and carbon dioxide (CO_2) after reductive ozonolysis.

Confirm the Answer Choices

Examine the answer options provided. The only option that includes formaldehyde, acetaldehyde, and carbon dioxide is option (d): Mixture of CH_3CHO, HCHO and CO_2.

Key concepts

Alkene Reactions

Alkene reactions form the backbone of many organic chemistry transformations. Alkenes are characterized by the double bond between carbon atoms, which is a point of high reactivity. This double bond opens up various possibilities for chemical reactions, including addition reactions, polymerization, and ozonolysis. In the case of ozonolysis, the double bond is attacked by ozone, which results in the cleavage of the bond and the formation of ozonides. This feature of alkenes makes them versatile starting points in synthetic organic chemistry.
Alkenes can undergo:

• Addition Reactions: Molecules add across the double bond, leading to the formation of different products.
• Ozonolysis: Double bonds are cleaved to yield smaller molecular fragments.

Understanding the position and nature of these double bonds allows chemists to predict and manipulate the outcomes of reactions to suit synthetic needs.

Ozonolysis Mechanism

The ozonolysis mechanism is an insightful process that reveals the reactivity of ozone with alkenes. When ozone ( O_3 ) reacts with an alkene, it forms an unstable intermediate called a molozonide. This intermediate quickly rearranges into a more stable ozonide.
Subsequently, the ozonide can be broken down into smaller molecules through reductive or oxidative workup:

• Reductive Workup: Uses reducing agents like Zn/H_2O to convert ozonides into carbonyl compounds such as aldehydes and ketones.
• Oxidative Workup: Employs oxidizing agents, leading to the formation of carboxylic acids instead.

The beauty of ozonolysis lies in its ability to break complex alkenes into simpler carbonyl compounds, making it a powerful tool for structural elucidation and synthesis.

Carbonyl Compounds Formation

Carbonyl compounds, which include aldehydes and ketones, are key players in organic chemistry due to their versatile reactivity and presence in numerous natural products. During reductive ozonolysis, the double bonds in alkenes are cleaved, and these reactions produce carbonyl compounds as primary products.
Key characteristics of carbonyl compounds include:

• Aldehydes ( R-CHO ): Produced when the carbonyl group is at the end of a carbon chain.
• Ketones ( R-CO-R' ): Formed when the carbonyl group is within the carbon chain.

In the presented reaction involving CH_3-CH=C=CH_2 , the breakdown into formaldehyde ( HCHO ) and acetaldehyde ( CH_3CHO ) highlights how the unique structure of the alkene dictates the carbonyl products formed. Studying these reactions equips students with the tools to synthesize critical intermediates for further chemical transformations.

Organic Chemistry Concepts

The study of organic chemistry explores the vast array of chemical reactions and compounds that form the basis of life and many synthetic materials. Fundamental to this study is the concept of how functional groups like alkenes and carbonyls participate in reactions, shaping the design and outcome of chemical syntheses.
Here are some crucial points:

• Functional Groups: Principal reactive parts of organic molecules that determine the pattern of reactivity.
• Synthetic Pathways: Strategies employed to construct complex molecules from simpler substances.
• Structural Elucidation: Analytical techniques, like ozonolysis, that unveil the component parts of organic molecules to understand their complete structure.

By mastering these concepts, students not only enhance their problem-solving skills but also gain a deeper appreciation for the intricate world of organic synthesis, enabling them to tackle complex chemical challenges.