Problem 208 - A Complete Resource Book in Chemistry for JEE Main

Question

Ozonolysis of an organic compound gives formaldehyde as one of the products. This confirms the presence of (a) a vinyl group (b) an isopropyl group (c) an acetylenic triple bond (d) two ethylenic double bonds

Step-by-Step Solution

Answer

The presence of a vinyl group confirms formaldehyde formation upon ozonolysis.

Step 1: Understanding Ozonolysis

Ozonolysis is a chemical reaction where ozone breaks down alkenes to produce carbonyl compounds such as aldehydes, ketones, or carboxylic acids. Analyze the products formed to determine the original structure.

Step 2: Identify the Role of Formaldehyde

Formaldehyde (HCHO) is the simplest aldehyde, formed when an alkene with a terminal carbon (CH2=CH2) undergoes ozonolysis. This indicates that the original alkene had a terminal double bond.

Step 3: Analyze the Options

Examine the options: a vinyl group (CH2=CH-), an isopropyl group, an acetylenic triple bond, and two ethylenic double bonds. Only a vinyl group can produce formaldehyde upon ozonolysis as it has a terminal double bond.

Step 4: Choose the Correct Answer

Since a vinyl group leads to the formation of formaldehyde during ozonolysis, the correct option is (a) a vinyl group.

Key Concepts

Formaldehyde Formation

Formaldehyde, also known as methanal, is the simplest form of aldehyde. It has the chemical formula \( CH_2O \).
During chemical reactions, particularly in ozonolysis, it serves as an indicator of specific structural features in organic compounds. When an alkene with a vinyl group undergoes ozonolysis, formaldehyde is one of the products. This occurs because the terminal carbon in a vinyl group (\( CH_2=CH- \)) is exposed, allowing ozone to effectively react.
The breakdown of the double bond results in the cleavage of the molecule into smaller products, formaldehyde being one of them when a vinyl group is present.
The formation of formaldehyde in ozonolysis is a telling sign that the original compound had a terminal double bond. Hence, recognizing formaldehyde among the reaction products is essential to deduce the presence of a structure like the vinyl group.

Vinyl Group Identification

The vinyl group is a fundamental structural element in organic chemistry. It is represented by the formula \( CH_2=CH- \). Its structure consists of a carbon-carbon double bond where one carbon is terminal (attached at the end of the molecule).
This configuration makes it uniquely reactive during chemical reactions such as ozonolysis.
Using ozonolysis, we can investigate the presence of different functional groups in alkenes. When a compound containing a vinyl group undergoes ozonolysis, it yields formaldehyde. This identification is crucial. Among all possible functional groups, the vinyl group's configuration makes it the only one capable of breaking down to form formaldehyde during ozonolysis. This process is analogous to putting together pieces of a puzzle, where each product formed helps identify the initial structure of the compound.

Alkene Reaction with Ozone

Ozonolysis is a fascinating reaction that involves the reaction between alkenes and ozone \( (O_3) \). This transformation is instrumental in identifying the structure of organic compounds. An alkene, characterized by a carbon-carbon double bond, reacts with ozone, leading to the cleavage of these bonds.
The reaction mechanism proceeds through an intermediate called an ozonide. This unstable compound then decomposes, usually under the influence of a reducing agent, to form carbonyl compounds such as aldehydes and ketones.
Understanding the process is vital for students, as it explains how structural features of the initial alkene, like position and presence of double bonds, influence the final products.

• This is why alkenes like the vinyl group can be identified through the detection of formaldehyde post-reaction.
• The reaction's selectivity and specificity make it a powerful tool for chemical analysis.

By following this mechanism, chemists can map back to determine the exact nature of the initial alkene.