Question

An unsaturated hydrocarbon was treated with ozone and resulting ozonide on hydrolysis gives 2-pentanone and acetaldehyde. What is the strocture of alkene? (a) \(\mathrm{C}_{3} \mathrm{H}_{7}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) (b) CC=C(C)CC (c) CC(C)=C(C)C (d)

Short answer

The structure of the alkene is (a) \(\mathrm{C}_{3} \mathrm{H}_{7}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\).

Step-by-step solution

Understanding Ozonolysis

Ozonolysis of alkenes involves the reaction of an alkene with ozone to form an ozonide, which upon hydrolysis produces carbonyl compounds (aldehydes and/or ketones). The position of the original double bond can be determined based on the fragmentation of the ozonide, as each fragment corresponds to a portion of the original molecule.

Analyzing the Products

The given products of the reaction are 2-pentanone and acetaldehyde. This indicates that the ozonolysis cleaved the alkene at a position that results in a 4-carbon fragment (2-pentanone after losing a carbon) and a 2-carbon fragment (acetaldehyde).

Determining the Bond Position

Since the longer fragment after ozonolysis is a 4-carbon chain with the carbonyl group in the second position, the double bond must have been between the second and third carbons of the original alkene. The smaller fragment being acetaldehyde means the other part of the double bond must have been at the end of the carbon chain.

Matching the Structure

The structure that matches this description is (a) \(\mathrm{C}_{3} \mathrm{H}_{7}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\). It is the only option that would yield a 4-carbon and a 2-carbon fragment upon ozonolysis.

Key concepts

The Intricacies of Organic Chemistry

Organic chemistry is a vast field of science that focuses on the study and manipulation of organic, carbon-containing compounds. At its core, it explores the structures, properties, and reactions of molecules that make up living organisms and synthetic materials. One type of reaction prominently featured in this field is ozonolysis, a process that allows chemists to break down complex alkenes into simpler carbonyl compounds.

Ozonolysis is instrumental in understanding the structure of alkenes by cleaving double bonds, altering the original molecule's configuration. This has significant applications in pharmaceuticals, agrochemicals, and the synthesis of organic materials. By examining the products of ozonolysis, chemists can deduce the nature of the unknown alkene, showcasing the detective-like aspect of organic chemistry.

Deducing Alkene Structures through Ozonolysis

Alkene structure determination is an essential skill in organic chemistry, which involves identifying the location of double bonds within a carbon chain. Ozonolysis plays a pivotal role in this investigative process. When an alkene is treated with ozone, it forms an ozonide intermediate that yields specific carbonyl compounds upon hydrolysis.

The resulting carbonyl compounds are like puzzle pieces that, when put together, reveal the original position of the double bonds in the alkene. For example, when an unsaturated hydrocarbon produces 2-pentanone and acetaldehyde through ozonolysis, the structure of the alkene is deduced by analyzing the length of the carbon chain and the position of the double bond prior to reaction. This reveals not just the presence of a double bond, but its exact location within the molecule, providing invaluable information about the molecule’s reactivity and potential transformations.

The Significance of Carbonyl Compounds

Carbonyl compounds encompass a class of organic molecules featuring a carbon-oxygen double bond, and include aldehydes, ketones, carboxylic acids, and more. These compounds are central to many biochemical processes and are also widely used in the synthesis of various organic substances.

In the context of ozonolysis, the carbonyl compounds formed offer clues about the original structure of the alkene. The simple molecules produced, such as 2-pentanone and acetaldehyde, tell a story about the alkene's architecture. This transformation highlights the importance of carbonyl chemistry in not only functional group interconversion but also in unraveling the complexities of molecular structure. Understanding their formation and reactivity is critical in fields ranging from pharmaceutical development to materials science.