Problem 12 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Total number of isomers, considering both structural and stereoisomers of cyclic ethers with the molecular formula \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}\) is

Step-by-Step Solution

Answer

There are 5 isomers for \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\).

Step 1: Understand the Molecular Formula

The molecular formula given is \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), which indicates it is a cyclic ether. A cyclic ether is a molecule that includes an oxide ring, meaning oxygen is one atom in a ring, and the rest of the structure is carbon and hydrogen.

Step 2: Determine Basic Structures

For \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), the possible cyclic ether structures involve a tetrahydrofuran ring or a substituted epoxy group such as a monomethyl oxirane. We need to consider possible ring sizes, including 3-membered (epoxy), 4-membered, and 5-membered (tetrahydrofuran) rings.

Step 3: Identify Structural Isomers

Structural isomers are different connectivity of the same molecular formula. For \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), potential structural isomers include 1,2-epoxybutane, 1,3-epoxybutane, and tetrahydrofuran.

Step 4: Consider Stereoisomers

Stereoisomers have the same structural formula but differ in the spatial arrangement of atoms. For 1,2-epoxybutane and 1,3-epoxybutane, cis and trans configurations must be considered due to the presence of ring strain or substituents. Each epoxy compound can have two stereoisomers.

Step 5: Count the Total Number of Isomers

Calculate each category: Tetrahydrofuran provides 1 structural isomer. 1,2-epoxybutane has two stereoisomers (cis and trans). 1,3-epoxybutane also has two stereoisomers. Adding these, you get a total of 5 isomers (1 + 2 + 2).

Key Concepts

Cyclic Ethers

Cyclic ethers are a fascinating group of compounds that contain an oxygen atom within a carbon-based ring structure. This unique setup results in a variety of chemical properties and applications.

These compounds can be found with different types of ring formations, making them quite versatile. For instance, in the molecular formula \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), we can get a 5-membered ring known as tetrahydrofuran or 3-membered rings like epoxides.

The presence of an oxygen atom increases the polarity of these rings, affecting how they interact with other molecules. This property is key in many chemical reactions, including those used in the creation of polymers.

• Common types of cyclic ethers include tetrahydrofuran and epoxides.
• They have significant industrial uses, particularly as solvents and intermediates in synthesis.

Structural Isomers

Structural isomers are different arrangements of the same atoms within a molecule, leading to distinct chemical compounds. They illustrate how versatile a molecular formula can be, lending different properties to each isomer type.

For \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), structural isomers include forms like 1,2-epoxybutane and tetrahydrofuran, where the atoms connect in unique ways. The number of potential structures a molecule can have is influenced by the ring size and the position of substituents.

• Different connectivity leads to different physical and chemical properties.
• Examples with the given formula include tetrahydrofuran, 1,2-epoxybutane, and 1,3-epoxybutane.
• Discovering each isomer requires understanding of chemical bonding and molecular interaction.

Stereoisomers

Stereoisomers are fascinating in that they share the same structural connectivity, but their atoms are oriented differently in space. This difference can dramatically influence the characteristics and behavior of a compound.

In the realm of cyclic ethers like \(\mathrm{C}_{4}\mathrm{H}_{8}\mathrm{O}\), stereoisomers become significant with compounds such as 1,2- and 1,3-epoxybutane. The orientation of substituents around the oxygen in these structures can lead to different isomeric forms known as "cis" and "trans".

• Cis and trans isomers can differ in properties like boiling point and polarity.
• Such differences make stereoisomers critically important in fields like pharmaceuticals.
• Understanding stereochemistry helps in designing molecules for specific functions.