 Hello students. Can you hear me audible? Okay. So today we are going to start a new chapter. We have finished any class class, right? Yeah. So today we are going to start a new chapter of organic chemistry, and that is isomerism. All of you write down the heading isomerism. A little bit we have discussed about it. In KBBI class. Yes or no? Just two minutes. Okay. So what is isomerism? See, first of all, isomerism is a phenomenon, basically, right? So it is a phenomenon in which a given molecule exists in different, different forms in which they have different structural formula and they have different physical and chemical properties. So it is the right on heading. First of all, I'll take one example and make you understand. It is the phenomenon in which a molecule exists in different structural formula, structural formula, and they have different physical or chemical properties. This phenomenon is isomerism. Okay. And the molecule which exists in different, different forms are called isomers. Okay. So for example, you see, we have a molecular formula say C3 or C2H6O. This is the molecular formula. If I ask you to draw the structure of this. Okay. Two possible formula of this you can write. One is CH3OCH3 which is obviously an ether. Another one is CH3CH2OH. Okay. So one is ether. Other one is alcohol. So obviously, we see ether and alcohol have different properties, right? They have different chemical properties, right? We know this alcohol is polar protic solvent. This one is polar or protic solvent. We have oxenhydrogen bond. There is an acetic hydrogen present in alcohol, but we do not have such hydrogen present in ether. So obviously, they have different properties. Obviously, their melting and boiling point will also be different, right? This phenomenon is isomerism, right? This phenomenon is isomerism. And what are these two called? These two are, these two are called isomers of each other. Remember isomers we always define in a pair, right? These are the isomers of each other. This is what we are going to understand. One more information I want to know. Have we finished this one? P block group 13 and group 14? No. So like 13 and 14 we haven't done, okay? So what I want you to do, you can start NCRT on your own. 13 and 14. There are things to mug up, okay? Nothing much to understand there in that particular chapter. So I'll take up one class to finish these two, 13 and 14, okay? So we'll do that in the last, obviously we have to do this chapter and then hydrocarbon and then in the last one class we'll have for, you know, this thing. Group 13 and 14. Today is 11th and then 18th we have one class, 25th. We have another class, right? What? Which chapter? It will take two class, I guess, okay? The school portion though we can finish up today itself, but for competitive exam it will take two class at least, okay? So we have four classes till now. 5th, 7th you are going to have the full, you know, 11th portion, 11th syllabus test, came on test, okay? So before that we are planning to wrap up everything, right? So four to five class max to max we'll have, okay? So we'll take two class for this, two class for hydrocarbon and then one class for PN, P block that we have two groups, right? So you just go through once, you'll get, you'll know about it, you'll get the information, okay? I don't know, you know, the exact information yet it is not disclosed, but yes, I guess it is J means need, CT and advance, all four type. So isomerism, the definition you understood, correct? Now, what is the classification of isomerism? What are the different types of isomerism we have? Isomerism, you see it is classified into two categories first, into two categories. One is structural and other one is a stereo isomerism, structural or constitutional isomerism, both are same thing, constitutional isomerism and other one is stereo isomerism. Further, structural isomerism also classified. The first one in this we have chain or nuclear isomerism. Second one we have positional isomerism, positional isomerism, third one we have functional isomerism, fourth one we have metamerism, ring chain isomerism and the last one we have tautomerism. Stereo isomerism further classified into two categories, classified into two categories, configurational and conformational. Configurational isomerism again further classified into two categories that is geometrical and optical. This is the classification we have for isomerism. Now, for your school exam, only structural they will ask. If you look at the entire portion, the chapter is quite big. We have configurational, these two are very important for comparative exam, conformational is also important. All these things are important but in the school exam they will give you this and to some extent geometrical isomerism. Optical isomerism will teach you hardly 10 to 15 minutes, not more than that. Have you done this chapter in the school? Yes. Tell me. Not a separate chapter. It's a separate chapter actually, not in hydrocarbons. They also do not have that much time, so they'll manage something. So what I'll do here, I wanted to know they have done optical in detail, like they have done optical in school? No, they haven't done. So that's what the thing is, they won't ask you this in the exam. So one more thing we can do, we can start with this structural today. We'll finish whatever we can do. This is not that big. We'll finish whatever we can do. They haven't mentioned structural. Okay, we'll see. I'm not getting. Anyway, let it be. We'll discuss it first. We'll see that in the last, let it be. So what I'm telling you for a comparative point of view, all these things are very important. So we are starting with structural isomerism today. Heading right down structural isomerism. What is a structural isomerism? It is a form of isomerism, a form of isomerism in which isomers, in which isomers have difference only in their, only in their atomic arrangements. Only in their atomic arrangements in the molecule. Molecular formula must be same. That is the necessary condition we have. So basically same molecular formula, but different structural formula. Same molecular formula, but different structural formula. This is a structural isomerism. Different different types we have. The first type right down is chain isomerism. So you see same molecule molecular formula is there for there for all kind of isomerism we have under this. This condition we have everywhere. Okay. With this, what is the other condition we have which defines chain isomerism. Okay. So write down. It is due to the difference in in the arrangement of carbon atoms constituting the chain constituting the chain. Okay. For example, you see what is the name of this compound CH3 CH2 CH2 CH3. It is N butane. Another one you see CH3 CH3 CH3. This one is N butane, normal butane. And this one is 2 methyl propane, the IUPG name if you see. Isn't it? If you look at the molecular formula, both are same only. But the number of carbon atom in the chain is different. You see the parent chain is this one here, which contains three carbon atom, but here we have four carbon atom. So chain isomers we define only when the number of carbon atom in the parent chain is different with same molecular formula. Keep that in mind. The parent chain should be different in the two molecules which has the same molecular formula. Then it is chain isomerism. Okay. Now you see this example here. CH3 CH2 CH2 CH3 CH2 CH3. I request all of you to write down a bit faster. CH3 CH CH2 CH3 and here we have CH3. One more we have CH3 CH3 CH3 CH3 CH3 CH3. All these are chain isomers. If you look at the name, it is N-painting. This one is 2 methyl butane. You can check the molecular formula is same. And this one is 2 comma 2 dimethyl propane. They all have same molecular formula. Okay. The second molecule, we also call it as isopainting. When we have at second last carbon, any methyl group is present. Then it is iso group. This group is actually iso group. So it is isopainting. Okay. This we call it as neo-painting. Neo-painting. When the second last carbon has two methyl group attached. So it is neo-painting. Obviously, if you see the number of carbon at the end of the chain. Here it is 3. Here it is 4. Here it is 5. All these are chain isomers of each other. Another example of chain isomers, you see. This one is also chain isomers of each other. Copy. Okay. So key point here is, which one is it? Oh yeah. I missed one thing. We have a double bond here actually. And you can place double bond here also. Once again, what two, three, four, five, not here. You can place it here. That's fine. So key point in this particular thing is what? That the size of parent chain must be different. That is a key point here. Write down size of parent chain. Size means number of carbon atom basically. Must be different. And same molecular formula that we have already. Right. No. If you do not write here double bond than the parent chain is ring only. No. So we have a double bond here. So for this molecule, the parent chain is this. Not the ring. Here we are double bond. So this is a parent chain. Size is different. Got it. Yeah. You can also revise nomenclature. Okay. We have done it already. You can also revise it. That helps you. Quick revision is required. Okay. So here we have the size of parent chain is different. The second type of structural isomerism is position isomerism. Positional. Here what happens? Same molecular formula. Obviously we have along with that. The other condition is it is due to write down. It is due to the different position. Different position occupied by by an atom groups. An atom group. Or any functional group. Any functional group. Right. Double bond and triple bond also you can consider under functional group. Right. For example, you see CH3 CH. To CH double bond CH2. CH3. CH double bond CH. Single bond CH3. So these two are positional isomers. Because the position of double bond is at first carbon. Here it is at second carbon. Okay. Second one is CH3 CH2 CH2. NO2. And CH3 CH CH3. NO2. The position is different. Okay. Condition here is what? The size of parent chain. Must be same parent chain. Must be same. Another point also you must write down. Functional group like functional group. Like. Aldehyde. Carboxylic acid. It's derivative also we can consider. It's derivative. Sinides. Do not exhibit positional isomerism. Why can't tell me. Then guys. Okay. So these functional group does not show positional isomerism, because we, if you remember, while nomenclature, while no writing down the name of these functional group, we always start the numbering from the carbon atom of this functional group. Yes or no. Remember that. First position is always given to the carbon atom of the functional group. Correct. Hence the position is fixed. That is first for all these functional group. Hence they do not show positional isomerism. Okay. We have functional isomerism. This one we have same molecular formula, but different functional group. Write down. In short, I'll write down here. Same molecular formula. Different functional group. Okay. Like the first example I have given you CH3, OCS3, ether, and alcohol. CS3, CH2, OH. These two are functional isomers. Aldehyde, CH3, C double bond O, OCS3, CH3, CH2, C double bond OH. Aldehyde and ketone are functional isomers. Okay. Methyl cyanide, CS3, CN, and CS3, NC. It is isocyanide. This is cyanide. Functional isomers. Okay. If you take this example, it is aliphatic alcohol, CH2, OH, but if OH is directly attached to the ring, it is aromatic alcohol. It is a derivative of phenol. This is also functional isomers. Okay. Copy this down. What previous condition? That functional group. Wait, I'll tell you. Simple. If you write down this molecule, CS3, COOH. What is the name of this compound? 1, 2, ethanoic acid. Okay. If you write down this CS3, C double bond OH. 1, 2, ethanol. If you write down this CS3, CH, CS3, C double bond OH. What is the name of this compound? 1, 2, 3, 2 methyl propanoic acid. So you see all these examples, what we are doing? We are always giving first position to the carbon atom of the functional group. Right. Means always first position is given to this. Hence, other position or other number here is not possible. That is the rule of nomenclature. Hence, the number of this carbon atom is always 1. It cannot be anything other than 1. Right. Hence, it won't show positional isomerism. If the position is different, then only position. No. No, you need to revise nomenclature for that. We are going by the rules of nomenclature. Like for OH, it is not true. If you have CS3, CS3, CH2, CH2, OH. 1, 2, 3. Sorry. 1, 2, 3. Propanol. It is. So functional isomerism is this different functional group present. The next one is, write down the next one is, okay, so we have done this sort of mechanism we will do in last. Okay. Next slide down. We have ring chain isomerism. The fourth one. So in this, as the name suggests, one compound is a cyclic ring, and other one is a cyclic compound, another one is a cyclic compound. Write down. It is due to, it is due to the different modes, different modes of linking of carbon atoms in this isomers contains isomers contains either open chain ring structure, open chain or ring structure. We can also write down for isomers, the degree of unsaturation should be equal. Okay. Like for example, if you have a molecule, CH3, CH double bond, CH2. What is the degree of unsaturation for this molecule? Degree of unsaturation for this molecule. One more example I'll show you. CH3, CH2, CH double bond, CH2 and cyclobutane. And we can also draw one more like this. Methyl cyclopropane. All these are ring chain isomers. Yes. Degree of unsaturation is one. One note all of you write down. If the ring chain isomerism is not mentioned, then we consider this under this, under functional isomerism. Preferably we take ring chain. If ring chain is not mentioned, then functional. Done. Okay. Next. The fifth one is metamerism. Metamerism is possible with polyvalent functional group, with polyvalent functional group. Polyvalent functional group means like we have ketone, examples write down. We can have ketone, polyvalent functional group, two valency we have, ether, two valency we have, thioether, two valency we have, amines. Right. This kind of isomerism we define, write down. It is due to, it is due to the presence of, presence of different alkyl group, presence of different alkyl group attached to, attached to the same polyvalent functional group. Okay. I'll write down this as this way. NH, I'll write down here. See this example. We have CH3, CH2O, CH2, CH3. Methyl, ethyl and ethyl both side we have. If I write down this one side I'll write down methyl, and other side we'll write down propyl. Different alkyl group attached to both side of the polyvalent functional group. So these two are metamers. Okay. Similarly, if you write down CH3, CH2, C double bond O, CH2, CH3, CH3, C double bond O, CH2, CH2, CH3, these two are also metamers of each other. Remember it is not positional isomers. Okay. It is always metamers when it is a polyvalent functional group. So preferably we'll write metamers. If metamers is not mentioned then we can think of positional. So first metamers and then positional. Okay. Now in this we have one more left that is totomerism. Totomerism we'll do it later. Okay. Not now. We'll do it later. After finishing the portion we'll start a reaction mechanism and then in that one we'll do a totomerism there. Okay. So these are the five types of structural isomerism we had discussed. Okay. After this we need to understand the stereoisomerism.