Isomerism - Definition, Structure, Applications, Functions, FAQs

Isomerism - Definition, Structure, Applications, Functions, FAQs

Edited By Team Careers360 | Updated on Sep 12, 2024 01:00 PM IST

Isomerism is the phenomenon in which more than one compound has the same chemical formula but different chemical structures. Chemical compounds that have identical chemical formulas but differ in properties and the arrangement of atoms in the molecule are called isomers. Therefore, the compounds that exhibit isomerism are known as isomers. There are two primary types of isomerism, which can be further categorized into different subtypes. These primary types are Structural Isomerism and Stereoisomerism.

When two molecules have exactly the same number of the same kinds of atoms, yet they have different chemical and physical properties, this is known as isomerism. Isomerism also takes into account timing and energy. Molecules are mobile entities that go through various rotating motions that change their shape, all of which require energy. As a result, specific molecules might be identical on one timeline or set of energy circumstances while being different or isomeric on another. Finally, an isomer must be an energy minimum; it must be found in a well of energy.

In this article, we will cover the topic (Isomerism). This topic falls under the broader category of (Some Basic Principles of Organic Chemistry), which is a crucial chapter in (Class 11 Chemistry).

Also read -

Structural isomerism

Compounds having the same molecular formula but different structures (manners in which atoms are linked) are classified as structural isomers. Some typical examples of different types of structural isomerism are given below:

  • Chain isomerism: When two or more compounds have similar molecular formula but different carbon skeletons, these are referred to as chain isomers and the phenomenon is termed as chain isomerism. For example,$\mathrm{C}_5 \mathrm{H}_{12}$ represents three compounds as follows:
    • Position isomerism: When two or more compounds differ in the position of substituent atom or functional group on the carbon skeleton, they are called position isomers and this phenomenon is termed as position isomerism. For example, the molecular formula $\mathrm{C}_3 \mathrm{H}_8 \mathrm{O}$ represents two alcohols:

  • Functional group isomerism: Two or more compounds having the same molecular formula but different functional groups are called functional isomers and this phenomenon is termed as functional group isomerism. For example, the molecular formula $\mathrm{C}_3 \mathrm{H}_6 \mathrm{O}$ represents an aldehyde and a ketone as follows:


  • Metamerism: It arises due to different alkyl chains on either side of the functional group in the molecule. For example$\mathrm{C}_4 \mathrm{H}_{10} \mathrm{O}$represents methoxypropane $\left(\mathrm{CH}_3 \mathrm{OC}_3 \mathrm{H}_7\right)$ and ethoxyethane $\left(\mathrm{C}_2 \mathrm{H}_5 \mathrm{OC}_2 \mathrm{H}_5\right)$
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It is the type of isomerism in which the compounds possessing same molecular formula differ in their properties due to the difference in their geomtery that is, due to the difference in the direction of attachment of same atoms or groups in their molecule. It is not shown by single bonded compounds like(C-C) due to free rotation.
Geometrical isomerism is shown by$[>\mathrm{C}=\mathrm{C}<],[>\mathrm{C}=\mathrm{N}-],\left[-\mathrm{N}=\mathrm{N}_{-}\right]$and cyclo alkanes.

Also read :

Geometrical isomerism in Alkenes and Cyclo Alkanes

  • Case I
    These compounds cannot exhibit geometrical isomerism


    These compounds cannot exhibit geometrical isomerism
  • Case II



Difference between Cis and Trans Forms

Cis

  • Cis is more reactive, but less stable form as the same species are on the same side, so steric repulsion increases reactivity and decreases stability.
  • The dipole moment of cis is more.
  • It has less melting point as same groups are on the same side.
  • The boiling point of cis is more.
  • The solubility, viscosity, and refractive index of cis is more. Trans

Trans

  • It is a more stable, but less reactive form as the same species are on opposite sides.
  • The dipole moment is mostly zero due to symmetry in the case of symmetrical alkenes.
    For example,
  • In case of unsymmetrical alkenes, due to little unsymmetric, there may be some dipole moment value as well

    For example, trans-2-pentene has some dipole moment value but is lesser than cis form.
  • It has more melting point than cis.
  • The boiling point of the trans form is less.
  • The solubility, viscosity, and refractive index are less than cis form.

Related Topics link

Geometrical isomerism in cycloalkanes

It cannot show geometrical isomerism as one carbon atom has two similar species 'A'.

Geometrical isomerism in Oximes and Azo compounds

  • In oximes

  • In azo compounds

    Here, the attached groups may also differ, that is, A and B.
  • When Ends are Different Number of geometrical isomers = 2n
    Here, n = number of double bonds
    For example,$\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{C}$
    Here, n=2
    Number of geometrical isomers $=2^n=2^2=4$
  • When Ends are Same
    (i) When n is an even number
    Number of Geometric Isomers $=2^{n-1}+2^{n / 2-1}$
    $\begin{aligned} & \text { For example, } \mathrm{X}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{X} \\ & \mathrm{n}=4\end{aligned}$
    Number of geometric isomers $=2^{4-1}+2^{4 / 2-1}$ $=2^3+2^1=10$0
    (ii) When n is an odd number
    Number of geometric isomers $=2^{n-1}+2^{\{(n+1) / 2\}-1}$
    For example, $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_3$
    Here, n=3
    Number of geometric isomersNumber of geometric isomers $=2^{3-1}+2^{(3+1) / 4\}^{-1}}$
    $$
    =2^2+2^1=6
    $$

NCERT Chemistry Notes:

Recommended topic video on(Isomerism)

Some Solved Examples

Q.1 The number of chiral centers in penicillin is:

(1) 3

(2) 4

(3) 5

(4) 6

Solution:

As we have learned

An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or groups of atoms.

As shown in the figure below, there are 3 chiral carbons in penicillin.

Therefore, option (1) is correct

Q.2 In the following structure, the double bonds are marked as I, II, III and IV

Geometrical isomerism is not possible at site (s) :

(1) III

(2) I

(3) I and II

(4) III and IV

Solution:

As we have learned

Geometrical isomerism is not possible at Site I as two identical methyl groups are attached to the same carbon bearing the double bond.

Hence, the answer is Option (2)

Q.3 Which of the following compounds will exhibit geometrical isomerism ?

(1) 1 - Phenyl - 2 - butene

(2) 3 - Phenyl - 1 - butene

(3) 2 - Phenyl - 1 - butene

(4) 1, 1 - Diphenyl - prop-1-ene

Solution:

As we have learned

Out of the given structures, only 1 - Phenyl - 2 - butene is capable of showing geometrical isomerism because it will show Cis–trans isomerism. Other structures have alkene at terminal carbon which does not show geometrical isomerism.

Hence, the correct answer is Option (1)

Conclusion

Isomerism is a key concept in chemistry that highlights the diversity and complexity of molecular structures. It occurs when compounds share the same molecular formula but differ in atom arrangement.

Isomerism arises from the fact that the atoms in a molecular formula can be organized in multiple ways to produce compounds with varied physical and chemical properties, known as isomers. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ.


Frequently Asked Questions (FAQs)

1. 1.What are the different types of isomerism?

There are two common types of isomers. The Constitutional isomer is a molecule of different connections — like given simple bracelets where the arrangement of red and green beads is different. The second type are stereoisomers. For stereoisomers the connection is the same, but the components are oriented differently in space.

2. 2.What is isomerism/What is meant by isomers?

Isomerism is a disorder in which more than one compound has the same chemical formula but different chemical properties. Chemical compounds have the same chemical formulas but differ in the structure and arrangement of atoms in this molecule called isomers.

3. 3.What is the difference between enantiomers and diastereomers?

Enantiomers are chiral particles that are visual and cannot be elevated. Diastereomers are stereomer compounds with molecules that are invisible to each other's images and cannot be contradicted. There are no mirror images above each other.

4. 4.How do you identify an isomer?

You can distinguish them by their combination patterns and how they take up space with three. Identify the isomers of the structure (constitutional) with their integration patterns. The chemical atoms are the same but are connected in such a way that they form different functional isomerism groups

5. 5.What is functional group isomerism?

Functional isomerism occurs when substances have the same molecular formula but different functional groups. There are three functional group isomers of which you need to be aware: alcohols and ethers. aldehydes and ketones.

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Questions related to

Get answers from students and experts

Hello Gagan!

Sachin Rana's YouTube playlist (62 videos) or NS Sir's organic chemistry on the Mohit Tyagi Channel that you will follow for JEE Advanced depends on your needs and the constraints of time left for the examination.

Sachin Rana's Playlist:

  • Familiarity: You've gone through topics such as GOC (General Organic Chemistry) and Isomerism; so, you might have to proceed with his YouTube videos if you feel it saves your precious time.
  • Efficiency: If you are comfortable with Sachin Rana's teaching style, sticking to it can enable you to cover up the remaining material quickly and efficiently.

NS Sir's Content:

  • Thouroughness and Coverage: NS Sir is very thoughtful in coverage; this could be perfect for JEE Advanced prep but may take longer (potentially up to November to complete).
  • The comprehensive approach: If you want to know more, even deeper, you can find that the NS Sir tutor's content may build a stronger base.

Important factors:

  • Time: If you do not have much time, you should finish with Sachin Rana.
  • Learning style: Take it as you like, about your teaching style, so if you learn well through in-depth material, it is more likely that NS Sir will help you.
  • Prep Level: Do you feel comfortable with the basics? If not, then what the NS Sir is saying is going to help you dig into some decent depth.

Anyways, it's about finding the right balance between depth and timeliness. Whichever you do, practice regularly and take mock tests for how much you've improved.

Thankyou!!

Hello aspirant,

Here's a breakdown of your options and factors to consider:

Option 1: Continue with Sachin Rana's videos

Advantages:

  • Familiarity: You're already comfortable with his teaching style and approach.
  • Progress: You've made progress in GOC and isomerism, building a foundation.
  • Time Efficiency: You might be able to complete the remaining chapters faster since you've already covered some basics.

Disadvantages:

  • Uncertain Completion Time: Completing all of NS sir's lectures might take longer than you anticipate, potentially affecting your preparation for the JEE Advanced.
  • Lack of Focus: You might find it difficult to switch between two different teaching styles and approaches.

Option 2: Switch to NS sir's lectures

Advantages:

  • Comprehensive Coverage: NS sir's lectures are known for their depth and clarity, ensuring a thorough understanding of all organic concepts.
  • Advanced Preparation: Focusing on NS sir's lectures could help you prepare better for the JEE Advanced level.

Disadvantages:

  • Restarting from GOC: You'll need to revisit some concepts you've already covered with Sachin Rana.
  • Time Investment: Completing all of NS sir's lectures might take longer than you currently have.

Decision-Making Factors:

  1. Your Current Progress: If you feel confident with your understanding of GOC and isomerism from Sachin Rana, you can consider continuing with him. However, if you want a more comprehensive and in-depth understanding, switching to NS sir might be beneficial.
  2. Time Constraints: Assess how much time you have before the JEE Advanced. If time is a major factor, sticking with Sachin Rana's shorter videos might be more efficient.
  3. Learning Style: Consider which teacher's teaching style resonates better with you. If you prefer a more structured and detailed approach, NS sir might be a good fit.

Recommendation:

Ultimately, the decision should be based on your individual preferences, learning style, and time constraints. It might be helpful to watch a few lectures from both teachers to see which one aligns better with your learning needs.

Additional Tips:

  • Supplement with Practice: Regardless of which teacher you choose, practice regularly to solidify your understanding and problem-solving skills.
  • Mock Tests: Take mock tests frequently to assess your progress and identify areas where you need to improve.
  • Seek Clarification: Don't hesitate to ask questions or seek clarification from your teachers or classmates if you have any doubts.

I hope this guidance helps you make an informed decision!

Completing organic chemistry (OC) from the Samarpan batch of MKA Sir on YouTube can be a good option for you, especially if you have already covered the basics of GOC and Isomerism. However, there are a few things to consider:

  • Scope of the batch: While the Samarpan batch covers most of the important topics in organic chemistry, it may not go into as much depth as a traditional classroom course. You may need to supplement your learning with additional resources, such as textbooks or online tutorials.
  • Your current level of understanding: If you have a strong foundation in GOC and Isomerism, you may be able to complete the batch relatively quickly. However, if you are struggling with these topics, it may take you longer.
  • Your learning style: If you are a self-directed learner who can work independently, you may be able to benefit from the flexibility and convenience of online learning. However, if you prefer a more structured learning environment, you may find it challenging to stay on track without a teacher or classmates.

Overall, completing organic chemistry from the Samarpan batch of MKA Sir on YouTube is a feasible option for class 12th JEE aspirants. However, it is important to be realistic about your expectations and to supplement your learning with additional resources as needed.


I hope this information helps you.






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