 In the previous video we saw how the inductive effect influences the stability of reaction intermediates like a carbocation, a carbon ion and a free radical. We know how carbocations and free radicals are electron deficient species so the electron donating groups or the plus i groups tend to stabilize them while electron rich species like carbon ions are stabilized when we attach them to electron withdrawing groups that is the minus i groups. Let's stir up the pot a little and let's see what happens if we mix it all up. In this question we are asked to identify the least stable free radical. Hey, what do we know about the free radical? Well in a free radical there are about 7 electrons around the carbon atom so it is an electron deficient species so the electron donating groups would help it get stabilized. But what do we have here? We have fluorine, chlorine and bromine atoms attached. Electronegative species, electron withdrawing groups that tend to withdraw electron density through sigma bonds and they show minus i effect. But who would have the highest minus i effect? The ones that's most electronegative because it would have the highest tendency to pull the shared pair of electrons towards itself. And hey, what is minus i effect? It is pulling the electron density through sigma bonds. So fluorine will have the maximum minus i effect and if it is pulling electron density from a poor free radical, would the free radical be happy? I don't think so. The free radical needs electron density to be stabilized but you roll three of them up pulling electron densities from it. So the one that would show the least amount of minus i effect would not destabilize the carbon free radical as much as the others, right? So since the minus i effect is in this order the most stable free radical would be the third one but but but we are asked to identify the least stable free radical which would be the first option. Let's move on to the next question. Here we need to identify the most stable carbon ion. Hey, let's just recall whatever we know about the carbon ion. It's a reaction intermediate which is negatively charged. There are eight electrons that are present around the carbon atom. So it is electron sufficient and also it has a negative charge. So it is an electron rich species. So in order to stabilize itself it would want to shed that electron density away but what do we have here? We have alkyl groups present around it. Alkyl groups are essentially electron donating groups. If we have a methyl group for example carbon being more electronegative than hydrogen would pull the electron density of the respective bonds towards itself. It would be all electron rich now and thus would push electron density in the chain or the ring that it's attached to. So it has a plus i effect. What about the second one? So the carbon that is attached to the ring has another methyl group attached to it. Methyl pushes electron density to this methylene group. It also has a tendency to push electron density. So overall it would have a stronger minus i effect. More electron density would be pushed forward through the sigma bonds. Can you guess about the third one? Yes, it would have the highest plus i effect. But wait, a carbon ion already has a lot of electron density and somebody is just pushing more electron density on it. Would it help stabilize it? Nah! So all three would be destabilized. But if I have to compare them and find out the most stable out of them I would look at the one that is least destabilized. So since the plus i effect of the methyl group would be the least it would destabilize the carbon ion the least and therefore this one would be the most stable out of them all. Let's move on to the next one. Arrange the following in the decreasing order of stability. We have carbon ions here. So why don't you folks try this problem yourself and then we'll do it together. Okay, carbon ions are electron rich species in order to get stabilized they would want to shed out electron density. So they would want to push out electron density through sigma bonds. So they would love to have electron withdrawing groups around them, right? Or the groups that show minus i effect. If I look at the first one the NO2 group attached does have a minus i effect. It does pull electron density towards itself. While in the second case we have the alkyl group which would push electron density through sigma bonds. So it is an electron donating group. It tends to destabilize the carbon ion. And what about the third case? Well, O minus has a strong plus i effect. So it tends to push electron density to the carbon ion. Hey, but this OH has a minus i effect. So why does O minus have a plus i effect? It's still O, right? It's still electronegative. Well, in case of the OH group the electronegative oxygen atom tends to pull electron density through sigma bonds and yes it has a minus i effect. But when we talk about O minus that is being attached to the carbon chain this O minus has a lot of electron density on it. It has a negative charge. So this would want to push electron density away as well and therefore O minus does have a plus i effect. If it is attached to a carbon chain or a methyl group I'm not saying the methyl group wouldn't show a plus i effect theory. Yes it would, but O minus would also have a plus i effect. And since it has a negative charge around it, it has a negative electron cloud around it it would be able to push more electron density on this side. And therefore it has a stronger plus i effect as compared to the methyl group. Interesting, right? Interesting how OH group has a minus i effect but as soon as you put a negative charge on that oxygen atom it gets all riled up. It gets all the electron density on itself and now it wants to push that electron density away through sigma bonds and it becomes a plus i group. Hence we see NO2 group has a minus i effect, CH3 has a plus i effect and this O minus has a strong plus i effect. We are talking about stability of carbons it does not want electron donating groups near it. So the most stable carbonyne would be the first one and the least stable would be the third one. Let's move on to the next question. Arrange the following in increasing order of stability. Why don't you try this problem yourself and then we'll do it together. Hmm, carbocation stability, carbocations are electron deficient species. So if somebody wants to donate electron density to it it would accept them wholeheartedly while if somebody wants to take electron density from it it wouldn't like them so much, right? If you look at the first case this carbon is attached to three methyl groups which are electron donating groups. So they push electron density to this carbon it gets all the electron density and it pushes it forward and this carbocation gets good amount of electron density. So this entire group has a plus i effect. Here the carbon directly attached to this carbocation has a methyl group attached to it. Yes, it donates electron density but would it be as good in donating the electron density as this group? No, right? Because it has a lot of electron density to donate. Correct. What about the third case? Here the carbon that is attached to the methylene group to this part, this carbon is actually attached to a more electronegative nitrogen atom. Nitrogen would want to pull the electron density of this bond towards itself and get a delta negative charge. This carbon gets a delta positive charge. Well, it becomes a polar of electron density. It would want to pull electron density via sigma bonds and show a minus i effect. So which one of the following would be the least stable then? The third one, right? And the most stable would be the first one.