 Right on next, second application mesomeric effect. This is the second electronic effect. Resonance is also an electronic effect. Resonance mesomeric effect, the second electronic effect after inducting effect. Mesomeric effect, we also call it as resonance effect. Both are same thing. Resonance effect. Like inductive effect will have plus i and minus i. What is plus i? What is plus i? Electron releasing. So here also we have plus m and minus m. Plus means electron releasing. So you can write this as plus m or minus m effect. Plus m is nothing but plus r and minus m is nothing but minus r. So plus m, group or what? These are the groups which can release electron pair. Electron pair donor. Plus m groups are electron pair donor. And what is the electron pair involved into this? Either pi bond or pi bond or donor pair. Because we know in mesomeric effect resonance, sigma bond does not involve pi electrons or lone pair. So plus m groups are those groups which has at least one lone pair present on the first atom. These are the groups which has at least one lone pair present on the first atom. First atom which, suppose we have a group, benzene pair, whatever group is attached, suppose NS2. NS2 has one lone pair. This is the first atom. It is a group that is attached with the benzene ring. The first atom of that group or the atom which attached with the benzene ring, if that atom contains at least one lone pair, it has plus m effect. It is very important. Plus m effect. I will give you the examples. But this is a general thing you should memorize. The first atom or the atom of the group which is attached with the ring, that atom must have at least one lone pair. Then it behaves as electron pair donor. Sir, the previous question, wouldn't there be mesomeric effect also? Sir, the previous question. This one? Yes. So it is the same. Whatever resonating structure we are drawing. For which we have done the RS for this. So this is mesomeric effect because it is releasing electron to the ring. The structure that you draw, that is mesomeric effect. Sir, what about the pure benzene? Sir, I will come to that. It is a plus m effect means that it has more tendency to release. No, no, no. Plus c. First of all, this effect will define for a group which is attached on any conjugated ring above benzene use of any other conjugated ring is possible. Conjugation should be there because for resonance, conjugation is the basic requirement. So plus m effect is defined for a group and these are the groups which can release electron to the ring. And it can release electron only when it has extra electron or available electron. Available electron means what? Lone pair of electron. Bond pair that cannot release. So this has at least one lone pair. So it can release this electron pair to this ring and this pi electron strip over here and then further you can draw the resonating effect. So plus m group are those groups which can release electron pair to the ring. Release, not withdraw. Condition is what? The atom must have at least one lone pair. Now what are the examples we have? We can have OH plus m group because oxygen has how many electrons? Two lone pairs on this. O CS3 plus m effect, okay. Next is NH2 plus m effect and R2. What is R? Alkyl group CS3, methyl, methyl, propyl, okay. And R2. We can write O C double bond O plus m like oxygen if you replace this oxygen with SH. This is also plus m, you won't get this anywhere but oxygen and sulphur you can do. R2 is this. That's why I wanted to do nomenclature first. R is this. Both alkyl groups are present. Means all this hydrogen you replace by this alkyl group, okay. See one thing you just try to understand here. This group means what these groups when attached to the ring. It donates electrons to the gas, okay. Now if you compare the plus m nature of O CS3 and O C double bond O CS3. Which one has more plus m nature? Why O CS3? Answer is correct but why? See, here first of all both will show plus m. Any doubt on this? Because it can show that. Here what happens, this lone pair is also involved in resonance with this oxygen. Pi sigma pi, lone pair sigma pi. This pi electron will withdraw this electron towards the side. Electron releasing tendency is less for this in comparison to this. See nitrogen has lone pair on it and this lone pair is in conjugation with this pi bond. Yeah, so what we can do, we can put this lone pair to bond pair like this. And this pi electron shift onto this target. So what, eventually what is happening, this NH2 group is giving electron to this ring. That's why it is plus m group. Sir, is that O C 83? Can't it also be O R? Because O R is also... O R, in general you can write O R. This is very important, you have to identify first the nature of the group. Then you can find out the other properties. So for plus m, the first atom must have at least one lone pair on it. Next one you write down NH, this one example also. NH which was there. These are plus m group, the group which shows plus m effect. Now can you tell me if you compare the plus m effect of this one and this one. Which one has more plus m effect? NH2 will have more. NH2 will have more, logic is same also. Okay, write down the example. What about halogens, X? X has lone pair. X has three lone pair, right? Does this halogen show plus m effect? Condition of plus m is there? So when this halogen attach with the range, any chlorine whatever it is attached to the ring. Since it has lone pair, it can show resonance like this. So it has plus m nature. It has plus m nature. Plus m nature it has, but its effective effect is this, minus i. Usually what happens, resonating effect dominates inductive effect. Means plus m always dominates plus i or minus i. Means effect of resonance is more than that of inductive effect. Means suppose if you have two molecules are there, both has carbocation. One carbocation is getting stabilized by plus m effect and other carbocation is getting stabilized by plus i effect. The one which shows plus m effect is more stable, right? Because plus m dominates plus i. Basically in general we can say mesomeric effect or resonance dominates i effect. So usually what happens, you see when oxygen attach here, for this example you see, nitrogen and oxygen bond we have, right? Nitrogen is more electronegative. Yes, so this nitrogen shows minus i also. If I ask you what all effects possible here, you can answer minus i and plus m. Both effects possible. But which one is dominating according to that will get the answer. But we know mesomeric effect dominates i effect. So plus m of NH2 dominates minus i nature. Yeah, only in case of halogen. Only in case of halogen its minus i effect dominates plus m nature. You must remember this is very important. Any doubt in this, right? So condition for plus m is the first atom must have at least one lone pair. Halogen has three lone pair but its minus i dominates, okay? Not plus m. Kind of exception. Usually plus m dominates minus i or plus i, okay? This example you see. Carbocation stability. Which one is more stable? That one. That one, how do I know? Second one. First one or second one? Second one. Second one. My second one. See in this what effect we have? What effect? Electronic effect. That series of plus i. Plus i. 3 degree carbocation. Minus m. Minus m. Minus m, why? Because its acceptance. There is no double bond. There is no conjugation. No, no, just one. This carbocation will have plus i. No, CS3 is giving electron. CS3, CS3 and C2H5 is this side. Right? It is alkyne group. No, alkyne group has plus i nature. It's CH2, CH3. Both are plus i effect. Alkyne group are, you are not the first plus. I'll share the video. So these are alkyne group and alkyne group are electron releasing. Plus i nature. So here we have only plus i effect. Here what we have? These two CS3 shows plus i. But because of this pi bond, this positive charge is in conjugation. Plus m. Right? This shows plus m effect. So effective, the plus m is effective over here. We can say the second carbocation is getting stabilized through. Resonance, mesomeric effect, plus m effect. And plus m dominates plus i. That's why the second one is more stable. Order is this. So can't we also just see it has more five moles? No, that is only possible for different decisions. RS of same volume. These are different volume. Because it is pi, sigma, vacant, not between. First type of conjugation. First type of conjugation. Plus m you can say also the resonance. So resonance is stable. Better rate resonance, not plus m. Resonance is 0. Resonance, don't write plus m. Resonance is very t. Or can we just say 1 pi bond, 0 pi bond? Where? No, 1 pi bond, 0 pi bond is only applicable for RS of same molecule or ion. That eight rules have given, you know. It is, you can compare RS of same molecule. These are two different molecules. What I'm telling you, we have two carbocation. We have to compare the stability. So first is I effect. Second is resonance. Resonance dominates I effect. Second one is more stable. That is it. So when you finish resonance, hyper conjugation and all, you'll get the, you know, questions in which I effect, hyper conjugation, resonance, all are taking place. According to the dominating effect, we'll find out the answer. Even in this one, I did not discuss plus H effect, hyper conjugation. Here plus I and plus H is also possible. And hyper conjugation dominates I effect. Resonance dominates hyper conjugation. So order is RHI, decreasing order. So you have to first identify what all effects are there and then you can compare. So with two LF examples, you'll understand. But you have to focus. So write down next minus M group, just reverse of this. Minus M group, you write down. It is electron with drawing group. Electron with drawing groups are those groups actually in which between first and second atom will have multiple bonds. Like suppose X is attached to the ring. I'll suggest you to memorize this general condition because there are many examples. It is difficult to memorize the nature of the group. Plus M, minus M, what is that? So the general thing you must remember, the first atom which attached with the ring, P H, and the second atom, why suppose? We must have multiple bonds between the two. It can be a double bond. It can be a triple bond. And if it is there, then why it is minus M? Because you see this example. If you have this ring, right? And one group say C H O is attached. C H O is this C double bond over H, right? So since this double bond is present, pi sigma pi conjugation we have, correct? So this oxygen takes electron there and this withdraws electron from the ring and that's why it is minus M. So this conjugation, if it is not there, then it cannot withdraw electron from the ring. Since carbon does not have lone pair, so it cannot donate the electron and this pi sigma pi conjugation we have, so it can, this pi goes onto this oxygen, then this carbon takes pi bond from the ring. So eventually it is withdrawing electron. So the condition is a reversal of minus M. Yes exactly. Minus M is electron withdrawing from the ring. Plus M is electron releasing. So minus M is the condition. But in first and second atom we must have double bond or if the atom which is attached with the ring has vacant orbit. Then again we have pi sigma vacant orbital possible. So this is also the type of conjugation here. If this three condition is there, then the box means vacant orbital and this box means vacant orbital. Okay vacant orbital. Example you write down NO2. You see NO2 the structure is this N double bond O. Double bond. Double bond. We can also write this aldehyde C double bond OH. Okay. We can also write C double bond OR. Okay. We can also write C double bond O. OR. C double bond O. OH. Okay. PH2. If PH2 is attached with the ring it also shows minus M effect because Goron has vacant T orbital. Goron has vacant P orbital. So PH2 is phenol. Phenol. Phenol. Phenol. It's not phenol. It's phenol. This is phenol. This is phenol. One open bond here. This group can be anything. Ph is this phenol. We can have cyanide C triple bond N. All these group shows minus M effect electron withdrawing nature. Then I'll write down some examples here. You have to tell me first what all effects are possible and which one is dominating. Okay. So for example you see you have benzene ring. NH2 group is attached. OCS3. C. Of C. CH. Sir, what is the difference if there is a plus sign effect or minus i effect and we can do something else. Sir, if we got plus sign effect dominating, does that mean stability or something? Yes. What do you want to say? Why you are asking that what all effects are found in that starting machine? Yes, it is not like what we get by finding out which plus sign effect or minus i effect. See, when you get that question, no. So, you should know what effect is taking place, then only you can come back. Right, it is not required here, suppose. If I ask you what effects possible here, what is the answer? Plus sign. Plus sign and minus sign. Minus sign, because nitrogen is more electro negative than this carbon. So, if I ask you what all effects possible, you can answer plus sign and minus i. But the nature of the compound is according to? Plus sign. Plus sign, because plus sign is dominating. Yes. So, when you find out the stability or anything, so you have to think according to plus sign effect, not minus sign. Okay. So, in this one, one more. NH C level bond O bar. Okay. Here, what all effects are there? Plus m and minus i. Plus m dominates. Here, what we have? Plus m minus i. Why minus i we have? Because carbon oxygen will have an electro negative rate difference. Yes. Right. And that is a permanent effect. So, that bond pair of electron is always shifted towards the more electro negative atom. Okay. What about this? Plus m dominates minus i C level bond O bar. Minus m and? No. Only minus m, because this carbon is sp2. This carbon is also sp2. There is no electron in it. Only minus m. Even here also, this is sp and this is sp2. So, minus m and minus i. Wait, wait. It is sp. It is sp. It is sp2. Sp is more electro negative. So, minus m minus i, but minus m dominates minus i. Here, it is plus m minus i plus m dominates. So, plus m or mesomeric effect always dominates inductive effect except in the case of what? Except in the case of halogen. So, if you have halogen attached on this, halogen has p lone pairs. It can show plus m effect. It can also show minus i effect, but minus i of halogen dominates plus m. In case of halogen inductive effect dominates. So, this is the next class. We will start with aromaticity.