Important Questions On Isomerism: CBSE Class 10th Term 2 Chemistry Exam

The CBSE Class 10 board exams are quickly approaching, and students are working with full dedication to perform well in their examinations. And why not! The CBSE Class 10 Term 2 board examinations are very important in a student’s academic career. It establishes the groundwork for their future studies, stream choices, subjects, etc. 

Chemistry is one of the subjects in CBSE Class 10 that requires students to pay close attention to because it encompasses the study of acids, bases, salts, carbon compounds, metals, and nonmetals. Students must understand the properties of several elements and study how diversely they can create compounds. As a result, this page discusses all of the important questions that might be addressed about “Isomerism” in Chapter 4 of the Chemistry NCERT textbook to assist students in their Chemistry Term 2 exam preparations. Students must use NCERT Solutions for Class 10 Science for concept clarity.

What are Isomerism and Isomers? Explain with examples.

Isomerism is a process in which two or more compounds have the same chemical formula but distinct chemical structures.

Isomers are chemical compounds with the same molecular formulas but different chemical characteristics and atomic structures in the molecule. As a result, compounds that feature isomerism are referred to as isomers. Use NCERT Solutions for Class 10 Science for better understanding of the concepts.

Students can understand the concept of isomerism with the following example.

Let’s evaluate the structural equations of the first three compounds of the alkane series, namely methane, ethane, and propane.

Also See: CBSE Class 10 Deleted Syllabus |  CBSE Class 10 Term 2 Exam Syllabus

These compounds can form the same structural formulas by rearranging the positions of carbon and hydrogen atoms in the molecules of these compounds. It indicates that even if the carbon and hydrogen atoms in the first three compounds of the alkane series are rearranged, the structural formulas will remain unchanged.

Take a look at the fourth compound of the alkane series, butane. Carbon and hydrogen atoms in butane can be organised differently to produce different chemical structures and, hence, different compounds.

Although n-butane and isobutane have the same chemical formula (C4H10), their structures are distinct. There is a long straight chain of carbon atoms in n-butane, whereas isobutene has a shorter straight chain of carbon atoms with a branch. In n-butane, no carbon atom is connected to more than two carbon atoms in the straight chain, but in the case of isobutane, one carbon atom is bonded to three other carbon atoms, and thus, both of them are called isomers.

Isomers are organic compounds with the same molecular formula but different structural formulas. This process is known as isomerism.

Briefly discuss the Types of Isomerism

The isomerisms can be broadly classified into the following two types, and these can be discussed as follows:

• Structural Isomerism
• Stereoisomerism

Structural Isomerism

Structural isomerism can also be referred to as constitutional isomerism. This phenomenon occurs when the isomerism is caused only by differences in the positions of atoms inside the molecule (without any reference to space) of the compound. In other words, these isomerism compounds have similar molecular formulas but different structural formulas. Because structural isomers may or may not include the same functional group, they are given different IUPAC designations. This sort of isomerism, which results from differences in molecular structure, includes:

• Chain or Nuclear Isomerism
• Positional Isomerism
• Functional Isomerism
• Metamerism 
• Tautomerism
• Ring Chain Isomerism

Stereoisomerism

Stereoisomerism occurs when isomerism is created by different positions of atoms or groups in space (In Greek, the term “Stereos” means occupying space). The structural formulas of stereoisomers are the same, but the physical positions of atoms or groups in the molecule are different in the compounds. Thus, In other words, stereoisomerism occurs in compounds that have the same molecular structure but with various configurations. Such types of isomerism can be further classified into two subcategories:

• Geometric Isomerism
• Optical Isomerism

Explain the different Types of Structural (Constitutional) Isomerism.

Chain or Nuclear Isomerism

Such a type of isomerism is created by the structural difference in the carbon chain that forms the nucleus of the molecule. As a result, it is known as chain, nuclear isomerism, or Skeletal isomerism. For example, the two butanes are known to have the same molecular formula (C4H10) but with different molecular carbon chain structures.

Positional Isomerism

Isomerism arises in compounds with the same molecular formula but with different chemical properties due to variation in the location of either the functional group, the multiple bonds, or the branching chain linked to the main carbon chain. Examples of positional isomers include isopropyl and n-propyl alcohol.

Functional Isomerism

When two or more compounds have a similar molecular formula but different functional groups, they are called functional isomers, and the process is referred to as functional isomerism. In other words, functional isomerism occurs when substances have the same molecular formula but belong to different categories of compounds.

Metamerism 

Such a type of isomerism arises due to the uneven distribution of carbon atoms on each side of the functional group of the molecule in a compound belonging to the same category. Methyl propyl ether and diethyl ether are examples of such isomerism.

Tautomerism

It is a form of isomerism wherein two functional isomers live in equilibrium. Tautomers are the two forms that exist in equilibrium. For example, an acetoacetic ester has two tautomers, one with a keto group and the other with an enol group. These two tautomeric forms are more stable and occur in greater abundance. Generally, 93 per cent of the keto group are more consistent while only 7 percent of the enol group exist in a less consistent form, i.e. lipid-soluble.

Ring Chain Isomerism

One isomer in ring-chain isomerism has an open-chain structure, while the other has a ring structure. They all have a different amount of pi bonds. C3H6 is an excellent form of this isomerism. Cyclopropane and propene are examples of ring chain isomerism.

Explain the two types of Stereoisomerism.

Geometrical Isomerism

The isomers, which have similar structural and molecular formulas but different arrangements of atoms or groups in space around the double bonds, are geometrical isomers. This phenomenon is known as geometrical isomerism. Compounds with the structure exhibit geometrical isomerism are:

Cis – trans isomerism: Isomers with similar atoms on the same side are called cis isomerism; when the same groups of atoms are present on the other side, it is called trans isomerism.

Optical Isomerism

Compounds with optical isomerism have comparable bonds but different atomic spatial arrangements, resulting in non-superimposable mirror images. Enantiomers are another name for optical isomers. The optical activity of enantiomers differs from one another.

As shown below, Dextro enantiomers spin the plane of polarised light to the right, whereas Laevo enantiomers spin it to the left. Use NCERT Solutions for Class 10 Science – Download Free PDF’s | AESL for conceptual clarity.

What is Ionisation Isomerism? Explain with an example

Ionisation isomers are compounds that produce distinctions in solution despite having the same composition. This phenomenon is known as ionisation isomerism. Ionisation isomerism refers to compounds that produce distinctions in solution despite having the same composition. When the counter ion in a mixed salt is also a potential ligand, it can remove a ligand, becoming the counter ion.

[Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4 are examples of ionisation isomerism.

Also See: CBSE Class 10 Study Material | CBSE Class 10 Syllabus

Conclusion

True learning occurs when concepts are understood. As a result, students must understand these questions well, as they are based on the topic “Isomerism” and focus on the students’ conceptual frameworks. Students can use the NCERT Solutions for Class 10 Science – Download Free PDF’s | AESL to help them grasp the answers. These solutions are available in PDF forms. Students can print out these solutions and revise them whenever needed. 

A solid understanding of concepts will also enable students to perform experiments and make the right diagrams in their CBSE Class 10th Chemistry Term 2 board and practical exams. Furthermore, performing well in the CBSE Class 10th Chemistry Term 2 exams would increase their overall score. Best wishes! and study hard for the exams.

FAQs

1. Define Isomerism as per Organic Chemistry.

Under organic chemistry, isomerism can be defined as a phenomenon wherein two or more organic chemical compounds have a similar molecular formula but distinct characteristics due to differences in atomic arrangement and the carbon skeleton (structural isomerism) or space (Stereoisomerism).

There are two types of isomerism:

• Structural Isomerism

Constitutional isomerism is another name for structural isomerism. Here atoms of isomers are bonded in many different ways and sequences.

• Stereoisomerism

Isomers and stereoisomers have the same number and type of atoms and bonds but differ in their orientation in space. After the Greek word stereos, these isomers are known as stereoisomers, which means “solid.”

2. What is the difference between Structural isomers and Stereoisomers?

Isomers can be defined as organic compounds with a similar chemical formula but different atomic configurations. The primary distinction between structural isomers and stereoisomers is that structural isomers share the same chemical formula but have various atomic arrangements. In contrast, stereoisomers share the same chemical molecular formula and atomic arrangement but have different spatial arrangements.

3. What exactly is Diastereoisomers?

Diastereomers are non-identical, non-mirror image stereoisomers. They arise when two or more stereoisomers have the same chemical molecular formula but distinct configurations at one or more (not all) of their equivalent (related) stereocenters. They do not form mirror reflections of one another. Diastereomers frequently contain compounds with ring structures. Diastereomers are commonly chiral and unique from one another. Typically, diastereomers may be recognised only when the molecule of the compound has two or more chiral centres.

4. What exactly are threo and erythro?

When a chiral carbon atom is present in a molecule, two configurations can arise in that compound and that is erythro and threo. When the same groups are present on the same side of the carbon atom, the configuration is erythro, and when the same groups are present on the contrary direction of the carbon atom, the configuration is threo.

5. What is the distinction between an enantiomer and a diastereomer?

Stereoisomers are classified into two types: enantiomers and diastereomers. Isomers that form mirror-like images and have non-superimposable chiral centres are examples of enantiomers. While on the other hand diastereomers have chiral centres that are not superimposable, they do not create mirror images. There could be significantly more than two stereocenters, based on the number of stereocenters.