 We have already talked about what inductive effect is and what are the nitty gritties related to it. In today's video, we will be talking about inductive effect and the stability of intermediates. Well, what do we really know about the intermediates? The intermediates are formed within a reaction and they get used up within a reaction, right? And, talking about the intermediates, what are the common intermediates that we usually find in a reaction mechanism? They are carbocation, carbonion and a free radical. If we dive a little deeper, we see how in a carbocation, the carbon atom has six electrons around it. Each bond has two electrons, right? What about the carbon ion? Well, here, each bond again has two electrons and two electrons make up the negative charge. So, the carbon atom has eight electrons around it. And in case of a free radical, there are seven electrons around the carbon atom. What does it really tell me? The species whose octet isn't complete is actually an electron deficient species. So, the carbocation and the free radical are electron deficient. While the carbon ion has a negative charge, it has a lot of electron density. It is an electron-rich species. We also know how the rate of a reaction depends on the stability of these intermediates. The more stable the intermediates, the faster they are formed and the faster the reaction takes place. So, if I really need to stabilize the carbocation and the free radical, I would want to attach them to electron donating groups, right? Why exactly? Because everything really wants to be neutral, to be stable. So, in order to stabilize them, I would need someone to push electron density towards them as opposed to what's needed by a carbon ion. A carbon ion has a lot of electron density. It really wants to shed it away to stabilize itself. So, it would need someone to take away this electron density. So, it needs an electron withdrawing group with it. How do I really relate it to the inductive effect? Well, the groups that tend to donate electron density via sigma bonds, that is, the groups depicting plus i effect, would stabilize the carbocation and the free radical? While the groups that withdraw electron density via sigma bonds, that is the minus i groups, would stabilize a carbon ion. Let's just go through a few problems to understand this better. If we look at this question, it asks us to identify the most stable carbocation. A carbocation is an electron deficient species. It needs someone who could donate electron density to it, right? So, here, if I write these ions in a more elaborative way, I can see how there's a methyl group present in each case. What do I know about the methyl group? In the methyl group, the carbon atom is attached to three hydrogen atoms. Carbon being more electronegative will pull the electron density of the bond towards itself. Oh, it became electron dense now. What would it do? It would try and push it out to the next attached group. So, a methyl group tends to donate electron density through sigma bonds. It is an electron donating group. Inductive effect, really, is a distance dependent effect, right? The farther away the donating or the withdrawing group is, the lesser is its effect. This is what we have already studied. So, let's just apply it here. The farther the methyl group is from the carbocation, the lesser help will it be able to provide, right? So, it's the closest in the third case. And therefore, it would provide the maximum support in the third case. It would help stabilize the carbocation, the best in the third case. So, the most stable carbocation would be the third one. Let's move on to another question, shall we? Here, we need to identify the most stable free radical. Free radicals are electron deficient species as well. So, what do I see here in the options? There's a methyl group on the left-hand side of the radical in each case. Methyl groups are electron donating groups. They donate electron density through sigma bonds and therefore, a plus i effect. So, that's the case in either case. How do I compare? Let's look at the right-hand side of the radical. In the first case, the carbon directly attached to this radical is also attached to three other methyl groups. Methyl groups are electron donating. So, this carbon is receiving electron density from three methyl groups. And if I try and compare it to the other two, in the second case, there are two methyl groups attached to the carbon that is directly attached to the free radical. It is also electron donating. But would it donate as much electron density through sigma bonds as the one in the first case? Not really because it has lesser donating groups attached to itself. What about the third one? In the third case, the carbon directly attached to the free radical is attached to just one methyl group. Of course, it will also donate electron density. It will push electron density through sigma bonds. But it wouldn't be as great as the first one. So, the first one is the most donating one and therefore, will help stabilize the free radical the most and thus, the most stable radical would be the first one. Identify the most stable carboxylate ion. It's an anion. Why don't you try this problem yourself and then we'll do it together. So, what's common in each case? This part, right? Okay, what do I know here? The carbonyl group directly attached to this negatively charged oxygen atom is actually an electron withdrawing group. Wait, how? Well, the carbon here is attached to a more electronegative oxygen atom. It has a partial positive charge. It's electron deficient. It would want to pull electron density through sigma bonds so it shows a minus i effect, right? But that's going to happen in either case. Yes, it will. What else do I see here? Hey, I see the methyl group attached to a carbon which is also attached to a hydrogen atom. I see some electron donating power here. The methyl group would donate electron density to the adjacent carbon but then push it to the next carbon and so on. So, this group essentially would donate electron density but that's also the case in each case. So, what we really need to focus on, it's the groups that are not similar in each case. They would decide which one of the following would be the most stable. Let's dive a little deeper and see if these groups are electron withdrawing groups or electron donating groups. In each case, the carbon is directly attached to a nitrogen atom. Well, nitrogen is more electronegative so it will be pulling electron density in each case. So, each of them will have a minus i effect. Okay, what else? How do I compare their minus i effects? If I look at third one, the nitrogen atom has a positive charge and electronegative atom having a positive charge. Would it really like it? No. You know, what does it really make it? It really makes it more electronegative. Wait, how? Well, it had an electronegative character, right? It had the tendency to pull the shared pair of electrons towards itself already. Now it has a positive charge. This would really help it pull more electron density towards itself. So it would pull the shared pair of electrons towards itself in a much stronger manner and therefore it has a strong minus i effect. What about the middle one? The nitrogen atom here is attached to a more electronegative oxygen atom. The electron density of this bond would be pulled by oxygen. This nitrogen gets a partial positive charge and what would this partial positive charge make this nitrogen do? Well, pull electron density and therefore it would have a stronger minus i effect as compared to the first case because in that case the nitrogen atom is attached to a less electronegative atom. So yes, it would pull electron density from carbon as well but not as strongly as compared to the other two. So the minus i effect looks something like this and therefore this group here has the highest tendency to pull electron density towards itself through sigma bonds. So it would help stabilize this negatively charged ion the best, right? So the most stable carboxylate ion would be the third one.