 Hello guys, you there? Okay, joined all of you. I don't know what happened, there was some technical issue. Okay, can we start? Okay, okay. So like I said, for an pi electron, do you see the molecular orbital that you have here, this contains unpaired electron. And because of this unpaired electron only, these are highly unstable compounds. Highly unstable compounds, right? The value of N can be anything, any natural number, zero, one, two, three, and so on. And here also it is right. Zero, one, two, three, so on, right? Anti-aromatic compounds are what? Anti-aromatic compounds, sorry, non-aromatic compounds are what? The condition for this, it is not cyclic, right? Or if it is cyclic, then not conjugated, not conjugated, not conjugated, right? And these compounds, non-aromatic compounds are actually the normal compounds at room temperature, normal compound, right? Means whatever compound at room temperature we have, those are like generally the stability of those compounds belongs to this category, okay? And in this molecular orbital does not form actually. Molecular orbital does not form, okay? Stability order of aromatic compound is maximum. Then we have non-aromatic and then we have anti-aromatic. This order is important. They've asked question on to this many times, okay? Now this is a theory, how to understand that the given molecule is aromatic or not, okay? So this is important and I'll give you so many examples, only these examples if you keep in mind, you can solve the questions in the example, okay? So I'm not going to give you the simple one like benzene ring and all, okay? For non-aromatic compounds, let's see some examples first. Like you see, these examples, these molecules are non-aromatic because it is not cyclic, okay? These molecules you see, these molecules, it is cyclic but not conjugated. It is also non-aromatic compound. Any sp3 hybridized atom if you have in the cyclic ring, it is non-aromatic. For example, you see this example, this question. This compound here, sp3 hybridized, sp3. This is also non-aromatic, okay? Any sp3 hybridized atom if you see, it is non-aromatic. Even this is also non-aromatic. Here we have conjugation, but this is sp3 hybridized, non-aromatic, okay? So non-cyclic compound are non-aromatic. If the compounds are cyclic, conjugation, if it is not there, it is non-aromatic. Even one more example, you see, if you have free radical present like this, this is also non-aromatic. Unpaired electron, non-aromatic, okay? What about this compound, you tell me? Anti-aromatic, non-aromatic or aromatic? This compound, positive charge. And if I put negative charge there, this one, this is aromatic or non-aromatic or anti-aromatic. Tell me, we have one, two, four pi electron, right? Pi electron also you must count, anti-aromatic. This has six pi electron, lone pair we count, aromatic, right? Pyridine, I have given you this example, pyridine. This lone pair is not involved in resonance. This compound is aromatic, okay? If you have oxygen present in the ring, see one thing just you remember, if any atom present, any atom present in the ring has two lone pair on it, then only one lone pair will count to define aromaticity. Just one thing you remember. If two lone pair present, then only one lone pair we count into the counting of pi electrons to define the aromatic behavior, right? Out of two, one lone pair will count and one pi bond is here. So one plus one, two, so we'll have four pi electrons here. And four pi electrons are anti-aromatic, understood? Even if you have compound like this, double bond and double bond, you see cyclic but not conjugated. It is non-aromatic compound. Tell me, cyclic benzene, B3N3, F6. Have you heard about that? The structure of inorganic benzene is this, right? All these nitrogen and boron has one-one hydrogen attachment, three bond. So one vacant P orbital, one vacant P orbital, nitrogen has lone pair, lone pair and lone pair. Can you tell me it is aromatic, non-aromatic or anti-aromatic? Yes, it is an aromatic compound because it has six pi electron here. It is an aromatic compound, B3N3, F6. That is inorganic benzene or borazole also we call it as. It is an aromatic compound. Why it is an aromatic compound? Because you see this lone pair can donate into the vacant P orbital of boron, right? So we have a conjugation. We have conjugation with six pi electrons, right? Aromatic. Now you see this example, all these are miscellaneous examples. Okay, if you write down properly and revise it before going into the exam, okay? You won't get anything more than this, whatever I'm going to give you today, okay? This structure you see, double bond, double bond, double bond and here we have positive charge. This is structure and this structure. Double bond, double bond, we have double bond here and here we have negative charge. What about this aromatic, anti-aromatic, non-aromatic? It is six pi electron, right? System is conjugated, it is aromatic, right? It has eight pi electron, system is conjugated, anti-aromatic. But again, this compound is not anti-aromatic. It should be anti-aromatic. What happens? You write down this point here, whatever I'm telling you write down. This point you write down. Monocyclic compounds, monocyclic compounds having atoms greater than equal to seven. Monocyclic compounds having atom greater than equal to seven will never be, can never be, never be anti-aromatic. They loses their plane, their plane and move out of the plane, out of the plane and becomes non-aromatic. Out of the plane means what? Non-aromatic. And why it happens? Because non-aromatic compounds are more stable than aromatic compounds. Because of this, what happens increases stability, right? This reason you let it be, okay? You write down in your notes, but you don't have to think on it, okay? What you have to remember? Monocyclic compounds greater than equal to seven if their number of atoms they have, then it won't be anti-aromatic ever, right? Because this molecule will lose its plane, overall molecule becomes non-planner and hence non-aromatic. But if they have aromatics, like we have six-pile electron, you see this is also seven-numbered, two, four, six, seven. But since it is aromatics, it is stable in this form because of aromaticity, it has some extra stability. This one is right, but when negative charge is there which make up, because of this it should be anti-aromatic which is highly unstable compound but to gain stability what happens? It changes its plane and convert into non-aromatic compound. So whenever you have number of atoms greater than equal to seven in a monocyclic compound, the molecule will be non-aromatic. Is it clear? Is it clear? Tell me, right? So this point you have to memorize. Can we move on? The structure will be like this, actually. The structure will be like this, something like this. Something like this where we have one, two, three bond and then one lone pair and negative, something like this. And other part will be another plane. Lone pair in pyridine is not counted because you see, see actually what happens in pyridine, we have nitrogen here, high bond present here like this. And how this pi bond forms, that is here you have to understand. In pyridine, how this pi bond forms because of overlap of these two orbital, then these two orbital and then these two orbital, correct? This is how the pi bond forms. So this p orbital all are parallel but the lone pair is present in a p orbital which is perpendicular to the ring of this, this ring that you have. Since this p orbital in which the lone pair is present is not parallel to these p orbitals, that's why it is not involving resonance, right? And since it is not involving resonance, we don't count this. Correct? Got it? Now another example you see, oxygen double bond, double bond. The nature of this compound. What about this? This is what? Anti-aromatic. How? You see how many atoms are there? Two, four, six, seven. There are seven atoms, monocyclic compound. It should be anti-aromatic but it is non-aromatic, change its plane. What are you doing? Got it? Vaishnavi, Sondarya, Saimir and Kushal. Seven membered ring, right? So it cannot be anti-aromatic. However it has, it follows four n pi electrons rule. Got it? Non-aromatic. What about this? These three structures you compare, the first one I have already drawn, we have oxygen. What about this? What about this? Is it a conjugated system? This one. See, it is a conjugated system because the boron has vacant p orbital present here. Right? So it is a conjugated system. How many pi electrons? Two, four, six pi electrons. Six pi electrons, so it is aromatic. Similarly here it is a conjugated system, six pi electron. This is not a conjugated system because this carbon atom is sp3 hybridized and hence it is non-got it. Tell me guys first. What happens in some compound? Double bond presents outside the ring. So in that case what we have to do? When double bond, double bond is outside the ring. See in this case, in this case, we'll draw a resonating structure, RS. For example, you see, if you have to write down the aromatic behavior of this molecule, double bond here, double bond here and we have double bond here, aromatic behavior of this molecule. So what we'll draw? We'll draw the resonating structure of this. We'll try to get this pi bond inside. So how do we draw that? You see, when this lone pair comes over here, this pi electron will jump here and we get this molecule. Double bond, this will be as it is O minus H plus. Now you see this molecule is conjugated with six pi electron, right? So this is aromatic. This is also aromatic. Suppose the compound is this, double bond O and this also if you draw the RS, you'll get this positive. This is aromatic with six pi electron. This is also aromatic, okay? What about this molecule? This molecule. This is aromatic or what? Draw this electron pair here. We'll have positive charge here, right? So we'll have two pi electron then aromatic. In this, you take this negative charge here, right? This lone pair here and this pi electron here, right? In that case, also you see it has six pi electron, aromatic in nature. See, non-aromatic is this. See, sign it. Non-aromatic is only possible when the conjugation is not there. Here we have conjugation. When conjugation is there, we have a very less chance of the compound to be non-aromatic. Right? So whenever you have double bond, try to draw the RS, RS in such a way so that you'll get aromatic compound. Okay? Basically, because it happens on its own. The molecule always goes towards stability. The shifting of electrons also takes place in such a way so that we'll get a stable structure. Right? So we'll see. In this case, you can ask me, so why don't you draw this pi electron here? Right? So if you draw this pi electron here, so we'll have then four pi electrons here. That makes the molecule anti-aromatic. Right? So that is one possible. Second thing, since oxygen is more electronegative, so this pi electron will shift here only. This tendency will be more. That's why it is aromatic. Got it? All these phenol, phenol you write, toluene you write, benzoic acid, all these compounds are aromatic compounds. All these, you write down the notes properly and you revise it. Okay? Another one, can I go to the next page? Tell me about this molecule. Tell me the nature of this. Tell me the aromatic behavior. Yeah, it's non-aromatic. However, if you count the number of pi electron, this 12 pi electron, right? So it should be anti-aromatic. But since the number of carbon atom is more than 7, so it is non-aromatic. Right? Now, few examples you see when we have multiple, multi-cyclic compound. In case of multi-cyclic compound, what we do? More than one. So in this you see, we have electrons and it is aromatic. Right? But if you have more than two rings present, right, like in this case, more than two rings present if you have, then what we do? This compound. So when we have more than two rings present, then we do not count this pi electron. This pi electron will not count. Or we can also say in other words that we only count peripheral pi electrons. Peripheral pi electrons means what? Suppose you are going from this way, right? So it is, you are starting from here. So all those pi electrons which comes, I will take a different color here. You see, peripheral pi electrons means what? You are starting from here. So what all pi electrons that we get along this route, only those pi electrons we count. Correct? So this pi electron is non-peripheral pi electron. Non-peripheral. And that is why we don't count this into aromatic behavior, right? So we have 1, 2, 3, 4, 5, 6, 7. So it has 14 pi electron. And it is aromatic in nature, what n is equals to. Got it? When we have more than two rings present in a molecule. Understood? Now you see another examples. This has 8 pi electron. Two rings will count all these pi electrons, 8 pi electrons. So it is anti-aromatic, right? This compound, what about this? See, for this molecule, all the carbon atoms are sp2 hybridized. So it is planar only. All the carbon atoms are sp2 hybridized. Tell me for this molecule, is it non-aromatic? Yes, it is non-aromatic. Oh, this one, tell me. It's non-aromatic. See, in this molecule, what we do, this is another type of molecule. See, what we have discussed, one is normal molecule molecule we have discussed. And then we discuss, in case of monocyclic compound, if the number of carbon atom is more than or equal to 7, then what happens? Non-aromatic, right? Then we discuss in case of multi-cyclic compound, right? More than two compounds if you have, then we count only peripheral pi electrons, right? Now, this is another type. If you have more than one cycle present, right? We have two cycle here. If more than one cycle present in the molecule, right? Multi-cyclic compound it is. And if multi-cyclic compounds, this compound is non-aromatic, right? Which is because of this sp3, sp3 hybridized carbon, right? Then what we do, if we get the multi-cyclic compound as non-aromatic, then what we'll do, we'll check the next smaller ring, right? We'll check the next smaller ring. So this is the outer periphery is this, right? And next smaller ring for this will be what? If you see, if you check this outer peripheral is this, this is sp3 hybridized, and hence it becomes non-aromatic. So if multi-cyclic compound, you get non-aromatic in first attempt, then we'll check the next smaller ring. So large ring is this, 6 to 8 carbon we have. Next smaller ring is nothing but the benzene ring, right? What is this? This is aromatic and hence this compound is aromatic. The whole compound is aromatic. This is not non-aromatic. What we do for this compound? For this compound, what kind of step you have to follow? I'll write down. The compound is of multi-cyclic compound type, okay? If outer perimeter or periphery, if you write, outer periphery is non-aromatic. Then what we do? We'll check the next smaller ring. Check the next smaller ring. If this is aromatic, then the compound will be aromatic. If this is non-aromatic, then again we'll check the next smaller ring. Next smaller ring. And this will continue till we don't get aromatic or anti-aromatic compound. Understood that? We'll keep on checking the next smaller ring and then next smaller ring and next smaller ring till we get the aromatic behavior or anti-aromatic behavior. Is it clear? What we are doing? We have checked the outer periphery, right? We got it as non-aromatic. Then we'll check the smaller ring here. Outer is this, the bigger ring is this. Next smaller ring is what? This particular ring, the benzene ring. Since the benzene ring is aromatic, it means the behavior of the compound is aromatic. Yes, they cannot be non-aromatic. We'll keep on changing. I'll give you some more questions on this. You see, then you will understand it. Suppose for this question, one and here we have done. Tell me for this one, for this molecule. Okay, now you'll see. Condition is what? The compound is multi-cyclic compound. And outer periphery, if you check, it is non-aromatic. Outer periphery is what? Non-aromatic. Then what is the condition we have? We'll check the next smaller ring. What is the next smaller ring we have here? The next smaller ring is nothing but this, which is again non-aromatic. And then we further check the next smaller ring, which is nothing but this. And this compound is what? Anti-aromatic. Hence the molecule is anti-aromatic in nature. I hope it is clear now. How it is aromatic you are getting, I do not know. Because it has 4 pi electron. How it is aromatic? Tell me, you think about it and tell me if you have any doubt. Just the, you know, the steps you have to follow. Sondarya, Kushal, Vaishnavi, Saim here. Did you get this? This example you see. Let me write down the question first. This is alpha. This bond is alpha. This bond is beta. Double bond we have here. Double bond, double bond. Here also we have double bond. Alpha, beta. The resonating structure of this you draw. You will get this. For this, if you draw the resonating structure. The question is, tell me the order of bond order of alpha and beta. A lot of questions. How do we do? You see that. So when the shifting of electron takes place like this. Okay. This ring you see. This ring has 6 pi electron. It is aromatic. This ring. This ring has 2 pi electron. It is also aromatic with 2 pi electron. And here we have 6 pi electron. Right. This ring has 2 pi electron aromatic. And this ring has 4 pi electron anti-aromatic. Right. Since both are aromatic here. So this molecule has more tendency to go into this form. This form is more stable in comparison to this form. Right. And since in the most stable form, the carbon-carbon bond order is 1. And here it is the lesser stable form here in comparison of this molecule. So the bond order of alpha is less than the bond order of beta. Tell me guys. Let me know if you read it out. All of you understood? All of you first. This is a conjugated system. Right. So either this pi electron will shift onto this carbon or this carbon. Right. If this pi electron shifts over here, then we get this structure. Correct. Yeah. Yeah. We'll finish this 4 week and then I'll give you the lunch. Give you the break. Okay. Not lunch. I cannot give you the lunch. Anyways. So let me finish this. When this pi electron jump over here onto this carbon. See there are 2 possibilities. Either it can jump onto this carbon or this carbon. Why I have shifted this pi electron over here that you try to understand. The case will be this. If this pi electron shift over here. And because of this shifting this part of the ring is aromatic with this lone pair. And this part of the ring is also aromatic. Right. But you imagine the reverse case. If you have negative charge here and positive charge here. Negative charge here. This part is anti aromatic 4 pi electron positive charge here. This part is also anti aromatic 4 pi electron, which is not in a stable condition. So this molecule has no tendency or this pi electron has no tendency to shift onto this carbon. Because then you are going towards the molecule is going towards unestability, anti aromaticity. That's why this pi electron will shift onto this carbon atom. We'll get this structure. Is it clear? This one. Tell me fast. Is it clear? The first one. Yes. Ramcharan Sundariya tell me. Now the same case you have here also. On both side we have cyclopropene only. So whether you shift this pi electron here or here the things will not change. Okay. So anyway you are going to get this molecule only in both kind of shifting. Now what happens with this shifting? This part becomes aromatic with 2 pi electron. This part becomes anti aromatic with 4 pi electron. Right. Since half of the part is anti aromatic. This molecule has comparatively less tendency to convert into this. Comparatively when we compare this and this molecule. To convert into this form and to convert into this form. Since it is highly stable because of aromaticity. This part this molecule will easily convert into this part. But this won't convert that much easily into this form. Right. And hence here we have single bond. Let's say the alpha bond order is close to 1. But beta will be close to 2 because of the anti aromaticity here. And that is why the bond order of alpha is less than that of beta. Now it is clear. So when bond order you know you can write down the bond strength also. Same order and bond length is what? Alpha greater than beta. There is one more term we use for this type of particular question. I have seen this question many where in different books. J. H. Advanced Level. They use a term called rotational barrier. Rotational barrier. Since alpha is going towards stability aromaticity. It means what rotational barrier of beta is more than alpha. Why? Because this pi electron won't rotate easily since it is going towards anti aromaticity. Rotational barrier of beta is more than that of alpha. This is a term we use. The concept is same. Why for alpha it is less because it is going towards aromaticity. Here half part is anti aromatic. Got it. So we'll take a break now. I wanted to take the class till 4. But fine. We'll take a break. We'll start at 3.30. This part will finish. One more condition is left of annulins. That will finish. There is not much left here. Hyper conjugation I have to discuss a bit. Then we can see the heat of hydrogenation and heat of combustion. For that hyper conjugation is required. We'll take a break now. We'll start at 3.30. Be there. Don't miss the last half an hour. One part of aromaticity is left. We'll finish that also. This part will be complete. All those examples you have written. The device when you are going for the exam. You won't get anything beyond this. That's why. Don't miss the last half an hour. Take a break. Can we start guys? There are a few 4.5 examples we'll discuss in this part here. Which is annulins. We are discussing aromaticity only. Annulins. This is actually a general name. Of the compounds which are cyclic conjugated hydrocarbon. Annulins are what? These are cyclic conjugated hydrocarbon. The name is annulins. Now example you see. This compound. Cyclic conjugated. Cyclobutadiene. Screen is blank. There are some technical issues. I am resending you the link. I am resending you the link. Just a second.