 Hello. Good afternoon. All of you, please type in your name in the comment box. Okay. See, today we are going to start. It's not basically a topic, right? It's not a separate chapter given in any book, right? But since we are going to have this kind of the concept that we are going to discuss today, this concept or this type of reaction we are going to discuss in the various chapter that is we have to study in organic chemistry. Okay. So since we already know that in organic chemistry, we have mainly reactions, right? So those reactions will have certain mechanism, correct? So what is the mechanism of a given reaction? How the reaction proceeds, right? What are the intermediates we have? How the intermediate forms? And again, the relative stability of the intermediate. Okay. So all these things mainly about reaction I am talking about for intermediates will have a separate glass. Correct. So today we are going to start the we are going to study about the mechanism of the reaction. Okay. So this is, so this is we have, we call it as reaction mechanism. Reaction mechanism. There are three, four different types of reaction we have. And in that, what is the mechanism of the reaction mechanism means what? Mechanism is nothing but the detail step by step description of one particular reaction, right? Mechanism is nothing but the explanation or detail step by step explanation of any reaction is the mechanism of that reaction. Okay. So suppose if I write down one reaction here, any reaction if I write down, the reaction is suppose rx, right? And if you have any nucleophile and u, right? Nucleophiles are negative charge reagent. Okay. So in this, the product we get here is R nu. And then x minus goes out. Okay. This is one reaction I have written over here to make you understand that what we are going to study today. Yes, Bharat, SN1, SN2 we will discuss today. So all of you please attend this session very carefully. Okay. Because later on what happens, suppose I will tell you here, there are three, four different reaction we have here. Suppose for example, if I take substitution reaction, okay. Substitution reaction, just a second, just a second I have an urgent call. For example, suppose if I say substitution reaction, okay. Elimination reaction, addition reaction. All these are different, different types of reaction we have. Okay. So this, you know, the explanation of this substitution elimination and addition, we will discuss here only. Right. Later on when we start hydrocarbon or other chapters, I will tell you that this reaction follows elimination reaction. This reaction follows substitution reaction. Okay. So there I will not discuss again the mechanism of these reactions. Okay. How the reaction proceeds. Okay. So it is, you know, it is very important for you all to understand the mechanism here itself. Okay. My job will also be, will also be easy next year in 12th class to make you understand the reaction mechanism. Right. The mechanism of reaction. Okay. So that's why if you, if some of you are not attending, do watch this session later on whenever you get time. Okay. And please attend this session very carefully. Okay. So coming back to this reaction, I have written one reaction here RxNu-RNu plus X-. This Nu- is a general thing I have written here. This is a nucleophile. Okay. Nucleophile. This nucleophile, electrophile will use very often in organic chemistry. Okay. So what is nucleophile? I will tell you. Nucleophile is what nucleo stands for nucleus. Right. This is nucleus and this is lover. Okay. So nucleophile means what? Nucleus lover. Nucleus lover. And we know the nucleus is what? Nucleus is positively charged. Right. Nucleus is positively charged. So hence positively charged species, this nucleophile are positive charged lover. Right. So this must have negative charge on it because opposite charge attracts each other. Right. So nucleophile is nucleus lover. Nucleus lover is positively charged. Right. Nucleus is positively charged. So obviously nucleophile, since it is a nucleus lover, it must be negative. So nucleophiles are what? Nucleophiles are reagent. Similarly, there is one more reagent we have. Okay. There is one more reagent and we call it as electrophile. Okay. So you write down all these things. Okay. So since it is an online class, so I will not dictate you each and every line. Right. Will not dictate you each and every line. So whatever I have, I am writing down here just to write down in a copy. Okay. Electrophile, similarly if I explain, electro stands for electron, file is lover. Right. So electron file is lover. So this electrophile is what? Electron lover. Electron lover. And since electron is negatively charged, so these electrophiles are what? These electrophiles are positively charged species. Okay. Positively charged species we can say, we can also say these are electron deficient species. That is also you must keep in mind. Whenever you define an electrophile, so electrophiles are electron deficient species or any positively charged species. Okay. Nucleophiles are negatively charged. So these are electron rich or all molecules which contains lone pair. Right. The molecules which contains lone pair or negative charge on it are called nucleophile. Okay. So if I write down the example H2O, H2O is a neutral molecule. Right. If I write down here BF3, BF3 is also a neutral molecule. But if I ask you which one is nucleophile and which one is electrophile, your answer will be what? H2O and BF3. Which one is nucleophile and which one is electrophile? Tell me. H2O is what? H2O is a nucleophile. And why it is a nucleophile? However, it is a neutral species. Okay. H2O is a neutral species. Then also it is a nucleophile. BF3 again, it is a neutral species or even I can write down here ALCl3 also. Right. So BF3 being a neutral species then it behaves as electrophile. This is also a neutral species nucleophile. Okay. So the point is this H2O molecule has two lone pair on it. Okay. Lone pair of electrons are the unbounded electron available on the atom. So it has two lone pair but BF3 does not have any lone pair. It has six electron. So it is electron deficient species. Okay. So BF3 since it is an electron deficient, so it has tendency to accept electron and that's why it reacts or it attaches with any electrophile. Correct. So this is what the point we have. So simply nucleophile and electrophile if you have to define, to define nucleophiles are the nucleus lover, negatively charged species fine but it, those molecules which has lone pair also that may also behave as a nucleophile. Ether may also behaves as a nucleophile sometimes. Right. Alcohol also may behave as a nucleophile. Okay. Electrophiles are what? Positively charged species, electron lovers. These are positively charged or electron deficient species like BF3, ALCL3 and all. Correct. So the point is the reaction which I have written over here. This reaction there are two molecules which are reacting here. One is this alkyl halide Rx and other one is nucleophile I have taken over here. Right. So in any reaction there are two different components. There are two different substances. Correct. One is, we call it as substrate. One is substrate and other one is reagent. Okay. So this reagent can be nucleophile or electrophile. Here I have taken the example of nucleophile. Is it clear? Right. So substrate and reagent. What are substrate? Substrates are those compounds which are being attacked. Right. Substrates are those compounds or molecules. Molecules which are being attacked. Regents are those molecules which attack substrates. Attack on substrate. So reagents can be molecules, can be ions. Right. So reagents are those molecules are ions which attacks on substrate and substrates are the molecule which are being attacked by the reagent. Okay. And the product we get here. Now here you see this nucleophile. This nucleophile if you see this reaction you forget all these things substrate, reagent, nucleophile, electrophile everything you just let it be. Just you see this reaction rx plus nu minus gives rnu and x minus. So x minus is leaving out. Right. So this is what this is a leaving group here. Right. The ions which goes out we call it as leaving group. Leaving group. So three, four terms we have discussed so far. Nucleophile, electrophile, substrate, reagent, leaving group. Right. Now if I talk about the different types of organic reaction. So next heading you write it down. Types of organic reaction. I have just now explained few terms that is you know that is that will be used that will use in in the discussion of these reactions. Right. Nucleophile, electrophile, substrate, reagent. Okay. That's why I have that's why I have explained these term first. Okay. So next you write down the types of reaction. Okay. So there are mainly three different types of reaction we have here. And the first reaction is substitution reaction. Substitution reaction. We also call it as displacement reaction. Displacement reaction. More often we use substitution only but displacement also we can use. The second one is elimination reaction. Elimination reaction. And the third one is addition reaction. Addition reaction. Okay. So these are the three main different types of reaction we have which will mainly study in organic chemistry. Okay. So we'll discuss these reactions one by one. Okay. So first reaction you write down the first type we have that is substitution reaction. Substitution reaction. In this type, I'll write down here, in this type of reactions, in this type of reaction, one atom or group, substrate molecule is replaced by replaced by another group. In this what happens in this, the carbon skeleton does not change. In this reaction, carbon skeleton does not change. It will be sp3 only. Okay. See rearrangement reactions. Also we have one type of condensation reaction also is there but you know what happens. These reactions, see condensation reactions are those reactions in which molecules like NH3, H2O goes out. Okay. These are not the main types. Okay. We can have, see reactions can be defined in various different categories. Okay. We are discussing about the nature of the reaction. Nature means what, nature means what, what all steps are involved, what are intermediates are involved in this reaction. On the basis of that, the reaction out of three types. Okay. Physical chemistry you must have studied. The reactions are classified into different, different categories. Like suppose, if I ask you on the basis of direction, the reaction are classified into two categories, reversible and irreversible. If you talk about the number of phase present, the reaction again are classified into two categories, homogeneous, heterogeneous. Okay. If the reaction like this, like this, the reaction are classified into various different categories depending on the, what basis we are taking. But here in organic chemistry, we are talking about the various steps involved in the reaction and how intermediates forms. Okay. So on the basis of that, the reactions are mainly classified into three categories. After these three, we have one more reaction that is rearrangement reaction. Okay. In which the rearrangement takes place. But that reaction we will discuss in all these only. Even in substitution also rearrangement possible. Okay. So that we will see in this section. Right. So substitution reaction, carbon, skeleton does not change. Correct. Now in this, the important thing here we have to discuss is nucleophilic substitution reaction. Okay. Next to write down nucleophilic substitution reaction. Now nucleophilic substitution reaction means what? Like nucleophile will attach at the substrate, the previous example that I have taken here, you see here, this is the nucleophile. And that nucleophile is attaching with this alkyl group. Correct. With the substrate. So it is nucleophilic substitution reaction. And in this, some, you know, leaving group goes out, like here we have X minus. Correct. So you see here, the next one we are talking about nucleophilic substitution reaction. Very important reaction we have nucleophilic substitution. Okay. In this reaction, you write it down. It is the attack of nucleophile, nucleophile, a saturated carbon atom, saturated carbon atom bearing substituent. Substituents are nothing but the leaving group. Bearing substituents known as leaving group, known as leaving group results in, results in substitution reaction. Or you can also write nucleophilic substitution reaction. So in which what happens here, one group or atom gets, get displaced. Right. For example, the previous example only I will write down. So the reaction here it is what Rx plus nu minus gives you Rnu X minus. So what happens here, the leaving group takes this bond pair of electron and goes out. Okay. Leaving groups takes this bond pair of electron goes out. This R become positively charged. This will be negatively charged when this go out and then this nucleophile attacks onto this R plus and we get this as a compound. So this is what one leaving group is getting displaced by this nucleophile. That's why it is substitution reaction. Substitution reaction. Right. Now you see the application of this. We can have many different nucleophile possible. Okay. And according to this nucleophile, we'll get different, different products here. For example, suppose if I write down this Rx, how this reaction is useful for various different topic that we are going to study is you see this. In this one you see, you can take many different nucleophiles. Suppose the first nucleophile I am taking OH minus negatively charged. Right. The second nucleophile suppose I am taking is OR minus here. Right. Another nucleophile I can take CN minus. We'll discuss the mechanism. First of all, I'm trying to make you understand what different, different products we get by this kind of reaction. Okay. CN minus. We'll get again NH3, NH3. Another one we have suppose RCOO minus. All these are negatively charged species. These all are, all behaves as a nucleophile. So what happens in all this reaction? This OH minus behaving as a nucleophile will replace this X minus in this reaction. Right. And the product here it will be what? ROH plus X minus. Here it will be ROR plus X minus. Then it will be RCN plus X minus. And it will be RNH2. RNH2 plus we'll get X minus, H plus. So HS minus we'll get. And then we'll get here ROC double bond O. Okay. Or to differentiate this here, write down this R dash. This R dash is this. Okay. So what all different products we are getting here? You see, we are getting first what we are getting? We are getting alcohol first. Then we are getting what? Ether. After that it is cyanide. And then we are getting amine. And this is one degree of mine. And then we are getting ester. So you see by this kind of reaction, we are getting many different products. Alcohol, ether, cyanide, amine, ester. Right. So all these chapters will, when we do this alcohol, ether and all, we'll discuss this that this reaction follows nucleophilic substitution reaction. Okay. So there I'll just tell you that this reaction is nucleophilic substitution reaction. Okay. We will not discuss this reaction again over there. Okay. So that you must keep in mind. Now you see, now here you see this all these here we have this is substrate. This is nucleophile or reagent substrate, reagent and living good. Okay. So now in this what happens, this is nucleophilic substitution reaction. Now the nucleophilic substitution reaction can be affected by the nature of nucleophile, its strength and concentration. Okay. This reaction, you write down here, nucleophilic substitution reaction, substitution reaction is affected by nature of nucleophile, nature of nucleophile, solvent, nature of substrate, because all these molecules are involved in this reaction. Okay. Nature of living group also we can write substrate and living group. Okay. How good the living group is all these factors influence the nucleophilic substitution reaction. Okay. Now this nucleophilic substitution reaction are also of two types. Okay. It is, it is nucleophilic substitution. It is classified into categories. The first one is, the first one is unimolecular nucleophilic substitution reaction. Now this is important. In short, we write this as nature in the sense of, see how, see when I talk about nucleophile. Okay. So nature of nucleophile means what, how, what is the nucleophilicity of that particular compound? What is the density of the negative charge over there? If it is more, its nucleophilic nature will be more. Okay. If the density of negative charge, suppose if I talk about NH3 and H2O. Right. NH3 and H2O. Or if I talk about NH, sorry, this one. Ph3 and NH3 we take. All these are nucleophile because it has one lone pair electron. We have, maybe it has a nucleophile. Okay. You see the electron density is same. Right. Now electron density is not same because the phosphorus size is more than that of nitrogen. So here the electron density is less. Okay. So this is a better nucleophile over here. Right. Similarly, we can also compare H2O. So when I talk about the nature of nucleophile, when I say it means how easily the molecule can attack onto the positive charge that we are getting here. That is what it means. Okay. Nucleophilicity basically. So unimolecular nucleophilic substitution reaction. In short, we write it as Sn1. Like this we write. Okay. Sn1 reaction. N stands for nucleophilic as is substitution and one is unimolecular. Okay. Sn1 is what? Unimolecular nucleophilic substitution reaction. Okay. Now this reaction you write down. This reaction proceeds in two steps. Two steps. This is the two step reaction. Okay. That step one is what? Step one is the formation of carbocation. Formation of carbocation. This is a slow step. And since it is slow step, it is the rate determining step. Determining step. Okay. Now you see how this reaction takes place in one step. Again, I will take the same example Rx. In the first step, the reaction is slow. Means this molecule is the living group. This atom is the living group. Takes this bond pair of electron. So this electron pair shifts over here. We will get R plus X has two electron and negative charge of it. Okay. So this is what? This is heterocyclic. This is heterolysis actually. Okay. One atom takes the bond pair of electron. Okay. So this is heterolysis. Okay. Heterolysis is right. So when this X takes this bond pair of electron forms negative charge and this R becomes positive charge. Okay. Now what happens? Since we are taking nucleophile over here, so that nucleophile will attack onto this carbocation positive charge atom in step two. Right. So step two is nothing but the attack of nucleophile. So what happens? This R plus will take this nu minus and the product we get here R nu. Okay. Now when the carbocation forms, the attack of nucleophile or the second step is very fast step. Very fast step. Okay. So slowest step or the slowest step is the rate determining step. Rate is nothing but the speed at which the reaction is proceeding. Right. So we will discuss about rate in detail when we do chemical kinetics. It is in 12th class. Okay. So we will not focusing on, here we will not focus on what is rate of a reaction. Okay. So rate of the reaction is nothing but the rate or the speed at which the reaction is proceeding. Okay. That we will discuss in chemical kinetics. Okay. Now in chemical kinetics also we will discuss a term that is order. Okay. So Sn1 reaction is nucleophilic substitution and one stands for, it represents the order of the reaction. Order of reaction. Okay. So this reaction follows, next you write down, follows first order kinetics. First order kinetics. Again this order term we will discuss in chemical kinetics. Okay. Just you remember two, three things in mind for order. It is an experimental quantity. Okay. It is an experimental quantity. Okay. Definition let it be for order right now because I do not want to go into that discussion now. It is not required here. Just for order you just keep in mind it is an experimental quantity. So in Sn1 when you say Sn1 it is nucleophilic substitution unimolecular first order reaction. Okay. So order of the reaction is 1. What represents the order over there? Okay. That you must keep in mind. Now when you write down the rate of this reaction rate is defined by the slowest step. It is the rate data mining step. Okay. It is RDS rate data mining step. Correct. So rate can be equals to any constant K into the concentration of the reactant species which is nothing but Rx. Okay. So this is the rate law expression. Okay. Again this is there in chemical kinetics. We will discuss this over there. Now here we are getting this positive charge which is a carbocation. Now what is carbocation? Tell me. What is carbocation? Carbon has only 6 electrons. Okay. Carbon with an extra pair of electrons. How carbon can have an extra pair of electrons? Then it will be negatively charged. Correct. So you see here. Next thing. See carbocation is what? Carbocation is a reaction intermediate. We discussed this in GOC also. Okay. Here I will just tell you a little bit about it. Reaction intermediate. All reaction intermediate are highly unstable, highly unstable and very reactive. All reaction intermediates, very reactive. For example, you see if you have this carbon atom like this, carbon, carbon, carbon. When the carbocation forms, heterolysis takes place between this carbon and halogen bond and here we get carbon positive charge on it with three different carbon it attached like this. Here the hybridization of carbon atom is what here? What is the hybridization of carbon here? It is sp3. Here it is sp3 and here it is what? It is sp2. Correct. Sp3 and sp2. So here the carbon atom is in this state it is sp3 hybridized, tetrahedral geometry. But when the leaving groups goes out to form a carbocation, its hybridization changes to sp2 and this becomes linear also. This becomes linear also. So when it is linear, then attack of nucleophile takes place. Correct. Now you see the SN1 reaction we have, it proceeds with the formation of a carbocation. So we will try to get the more stable carbocation always in this reaction. So we will try to form, we will always try to form more stable carbocation. So first we will get which one Marath? Which one is not planar or linear? The carbocation is planar, right? Carbocation is planar. Yes, carbocation is planar. Carbocation is planar because it is sp2 hybridized. So I will come back to this planar part again. Just give me some time. We will always try to form more stable carbocation. And what is the order of stability of carbocation we have? We know this benzyl almost equal stable. Then we have 3 degree carbocation, 2 degree, 1 degree and at last we have methyl carbocation. This is the order of stability of carbocation. So now when this is the order, so if you have any 2 degree carbocation forming by the elimination of living group, right? And if it is possible that by any means you can shift this 2 degree carbocation into 3 degree carbocation, right? So first we will do this a rearrangement and then the reaction takes place, right? Point here it is what we always try to form more stable carbocation. If the carbocation is 1 degree, then we will try to form 2 degree or 3 degree carbocation if it is possible, otherwise we let it be, okay? So for example you see here if I write down this molecule say we have example I will write down. And one more thing this carbocation are electron deficient that also one of the property we have you write down it is electron deficient reaction intermediate electron deficient. For example you see if I have this CH3, CHBr, CHCH3, CH3 and the nucleophile we are taking suppose OH- what is the product in this we get 2-methyl 2-butanol 2-methyl butane to all, correct? So all of you are getting 2-methyl 2-butanol, okay? So now you see how this reaction proceeds. First of all what happens the living group goes out, okay? So the reaction is what? The reaction is SN1, okay? So SN1 reaction we are assuming the first step is what? The living group goes out and we get CH3, CH, CH, CH3, CH3 and here we have Br and when the living groups goes out we will write Br-negative, okay? And we get what? CH3, CH, CH, CH3, CH3 and here we have the positive charge on it, okay? This carbocation is 2-degree carbocation, right? It is 2-degree carbocation and we know what 3-degree carbocation is more stable than 2-degree carbocation. So what happens here you see that since here we have one hydrogen if this hydrogen comes onto this carbon atom if suppose if I write down the hydrogen bond like this with this carbon like this if this hydrogen take this bond pair of electron and this H-minus will attack onto this carbon atom then what happens you see? This will get CH3, CH2, CH, CH3 and CH3. Now from here since hydrogen has taken bond pair of electron so this carbon will have the positive charge, right? Now you see this carbon atom is tertiary 3-degree which is a more stable carbocation. So this is a conversion of 2-degree to 3-degree carbocation. This kind of shifting we call it as 1, 2 hydride shift. You must have studied this 1, 2 hydride shift, correct? So now because of this kind of shifting the 2-degree carbocation converts into 3-degree which is a more stable carbocation. Now on this only the nucleophile which is OH-minus will attack onto this and the product will be CH2, CH3, CH, CH3, CH3 OH, okay? So it is 2-methyl butane to all because of the hydride shifting, okay? 1, 2 hydride shifting. So this kind of shifting is important in SN1 reaction. We are talking about SN1, not SN2. There is no H here, right? There is no H here, fine. We do not have H here also. We do not have H here. We do not have H here by mistake, right? So this is the answer we have. Your answer was correct, okay? So now coming back to the another part here which is again important that is stereochemistry of SN1 reaction. That is why I have started in the last class stereochemistry of SN1 reaction, okay? So you will not understand this right now, okay? So let it be this part, okay? So what you will do, we have to discuss this also here, stereochemistry of SN1 reaction, right? Only one thing you try to understand here, only one thing you see. In detail, we will discuss this when we finish stereochemistry, okay? We will come back to this again. Suppose we have C, any halogen atom X, here we have phenyl, here we have CH3, here we have hydrogen, okay? Now when the leaving groups goes out, minus X minus, we will get this pH, H and CH3 with positive charge onto this carbon atom. This is sp3 hybridized tetrahedral. This is sp2. It is planar. Now when it is planar, the attack of nucleophile, okay? Any nucleophile can be from any site, right? So if you have a nucleophile say OH minus. Since it is a planar molecule, so this nucleophile may attack from the top or from the bottom since it is a planar molecule, correct? So when it attacks from the top, you will have a definite molecule and from the bottom also you will get a definite molecule. Both will be different from each other, okay? So actually you see what happens, little bit of optical isomerism, I'll explain you over here. This carbon atom, can you tell me what is this carbon atom? Since I guess all of you have started a bit of optical isomerism also, stereochemistry also. What is this carbon we call it as? Have you heard about chiral carbon or something? Chiral carbon, chiral molecule, okay? So I think Kormungala guys have started this of it, okay? Anyways, anyways. So I'll just give you a brief introduction here, right? Because it is a part of stereochemistry, so that's why we have to study that particular part first. See chiral carbon or dose carbon, chiral carbon are sp3 hybridized carbon, sp3 hybridized carbon, which has different groups. So when I write down this carbon, suppose we have chlorine, OH, CH3 and H here. So this carbon is sp3 hybridized, okay? And when all the atoms are different, you see chlorine, OH, CH3 and H, all these four groups are different. So this is a chiral carbon, right? This is a chiral carbon means chiral carbon or dose carbon in which like those carbon which are sp3 hybridized and have all four atoms or group different, okay? So for example, you see if I write down this molecule, CH3C, CL, OH, CH, double bond, CH, CH double bond, suppose BR we have here, here we have CH3 and CHCCH3, CH3 and here we have H. In this molecule, it tells me how many chiral carbons are present. In this molecule, how many chiral carbons are present? Bharat, Gargi, RMN, here we have five bonds, right? So you just, how many chiral carbon? This is CH3. The last one is CH3, CH3, H. How many chiral carbon you are getting? Only one. Now coming back to this, what is the condition for chiral carbon? Carbon must be sp3 hybridized with all different four groups or atoms, right? So this carbon is sp3 hybridized, but we have three hydrogen present. So this is not the chiral carbon. This carbon, again it is sp3 hybridized and four groups are what? One is chlorine, other one is OH, third one is methyl and fourth one is this whole group, right? So this is one of the chiral carbon we have, right? So this is the one chiral carbon we have. This carbon is sp2, not possible. This carbon is sp2, again, not possible. This carbon is what? sp3, correct? This carbon is sp3. So we have one group is OH, other one is H, third one is this group, and fourth one is this whole group. So this carbon is also chiral carbon. Fifth one is sp3 hybridized, but since both groups are methyl only, so this is not a chiral carbon. So we have two chiral carbon possible here. Is it clear? Tell me how many chiral carbons are present in a benzene thing? How many chiral carbons are present in a benzene thing? The second one you see. You have to see two conditions you have to apply, Garry. First of all, the carbon must be sp3 hybridized, okay? And all atoms are, because carbon is tetravalent, right? Carbon is tetravalent. So we can have four different, four groups attached to it, okay? These four groups must be different, P, Q, R, S. If the carbon, sp3 hybridized carbon, attached with four different atoms or group, then only it is chiral carbon. That's what the condition is. So you have to check, you have to, you know, cross check both conditions, sp3 and four different group, correct? That's what I have applied for each of these carbon atoms, and you will get two carbon atoms on the chiral carbon. Understood? So if somebody asks you how many chiral carbon are present in a benzene ring, right? So in benzene ring, none of the carbon atom are sp3 hybridized, correct? All are sp2. So that's why there is no chiral carbon present into this. Zero will be the answer, correct? Now coming back to this question now, okay, chiral carbon. And one more thing, let me tell you, those who have studied a bit before in the school or by yourself only, you understand one thing very clearly over here, okay? chiral carbon.