Question

An alkene 'A' contains three \(\mathrm{C}-\mathrm{C}\), eight \(\mathrm{C}-\mathrm{H} \sigma\) bonds and one \(\mathrm{C}-\mathrm{C}\) \(\pi\) bond. 'A' on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of 'A'.

Short answer

The IUPAC name of 'A' is But-2-ene.

Step-by-step solution

Identify the Composition of Compound A

Since compound 'A' has 3 \(\mathrm{C}-\mathrm{C}\) bonds, it indicates there are 4 carbon atoms present in a chain (three single \(\mathrm{C}-\mathrm{C}\) bonds + one double \(\mathrm{C}=\mathrm{C}\) bond, indicating an alkene).

Determine the Structure Using Hydrogen Count

Compound 'A' has eight \(\mathrm{C}-\mathrm{H}\) bonds indicating the presence of 8 hydrogen atoms. Together with the 4 carbon atoms, this suggests a formula of \(\mathrm{C}_4\mathrm{H}_8\), typical for alkenes with no rings or additional elements.

Understand the Ozonolysis Products

Ozonolysis cleaves the double bond in alkenes and results in products based on the alkene structure. Here, 2 moles of aldehyde are noted, each with a molar mass of 44 u, which corresponds to acetaldehyde (\(\mathrm{C}_2\mathrm{H}_4\mathrm{O}\)).

Relate Products to Original Structure

Given the products are two acetaldehyde molecules, it shows that the original alkene 'A' must have been \(\text{But-2-ene}\), with the \(\mathrm{C}=\mathrm{C}\) bond between the second and third carbon, cleaving to form two identical aldehyde molecules.

Verify IUPAC Naming

Based on the structure (\(CH_3-CH=CH-CH_3\)), we deduce the IUPAC name for 'A' as But-2-ene, aligning with the presence of a \(\mathrm{C}=\mathrm{C}\) at the 2nd position in a 4-carbon chain.

Key concepts

Ozonolysis

Ozonolysis is a fascinating chemical reaction that involves breaking down alkenes using ozone. This process results in the cleavage of the double bond in the alkene, producing carbonyl compounds, such as aldehydes or ketones. In the exercise solution, ozonolysis is used to identify an alkene by the products formed after the reaction. To perform ozonolysis, ozone (O_3) is added to the alkene, targeting the carbon-carbon double bond (C=C). The reaction mechanism involves the formation of an ozonide intermediate, which decomposes to give the carbonyl products. Two main steps characterize this reaction:

• Addition of ozone to the double bond
• Decomposition of the ozonide to carbonyl compounds

In this exercise, ozonolysis of compound 'A' produced two moles of acetaldehyde. This indicates that the double bond was located between two identical carbon chains, as observed in but-2-ene. By analyzing the products, one can deduce the structure and the location of the double bond in the original alkene.

Alkene Structure

Alkenes are hydrocarbons characterized by the presence of at least one carbon-carbon double bond. This double bond is crucial because it influences the reactivity and basic properties of the alkene. In the exercise, the "C=C" bond is identified as the structural center for compound 'A'. The general formula for acyclic alkenes is C_nH_(2n), which demonstrates the presence of unsaturation due to the double bond. For an alkene like but-2-ene, there are four carbon atoms and a total of eight hydrogen atoms, forming a simple linear structure:

• Four C atoms with three single and one double bond
• Eight H atoms connected to C atoms through single bonds

Understanding the alkene structure helps predict its chemical behavior, such as the types of reactions it can undergo, including ozonolysis. In the exercise, focusing on the molecular formula and the product of reactions allows the determination of the alkene's identity and naming according to IUPAC standards.

Sigma and Pi bonds

Sigma (σ) and pi (π) bonds are essential components of molecular structures, especially in alkenes. Each type of bond has unique characteristics that influence the properties and reactivity of a molecule. Sigma bonds are the strongest type of covalent bond, formed by the head-on overlap of atomic orbitals. Each single bond in an alkene, including C-C or C-H, is a sigma bond. These bonds provide the framework for the molecule's structure, allowing for rotation along the bond axis. Pi bonds, on the other hand, are formed by the side-to-side overlap of p orbitals. In alkenes, the pi bond is the second bond in a carbon-carbon double bond and lies above and below the plane of the molecule:

• Contributes to molecular rigidity and restricts rotation
• More reactive than sigma bonds, especially in addition reactions

In the problem's context, understanding that the alkene has one C-C pi bond helps identify how it can participate in reactions like ozonolysis. The presence of sigma and pi bonds explains the typical bond configuration and reactivity patterns of alkenes.