 To understand the inductive effect, let's start with a simple butane molecule. Now, butane is non-polar, non-polar, what do I mean by this? Well, if you look at the electrons in this carbon-carbon bond, let me go ahead and name this as C1 and C2, let me also call this the C3 and the C4 carbon atom. So if you look at the electrons in this carbon-carbon bond, these electrons are attracted to the nucleus of two identical carbon atoms, right? So therefore the force of attraction that these electrons are going to feel is going to be equal and opposite. So the electrons in this bond are actually going to be equally shared between these two carbon atoms. And similarly, even the electrons in this bond and even in this one, all of these electrons are going to be equally shared. So there won't be any positive or negative charges in this molecule. And that's why we call this non-polar. Now let's see what happens if I add, say, a chlorine atom to this butane molecule. Now do you think the electrons in this carbon-chlorine bond, do you think that these electrons are going to be equally shared between the carbon and chlorine atom? Of course not, right? The electrons out here are now attracted to two non-identical atoms. So therefore the force of attraction that it's going to feel is not going to be equal and opposite. So the electrons out here will either be more closer towards the chlorine atom or towards the carbon atom, right? So what do you think? Do you think these electrons are going to be towards the chlorine side or towards the carbon side? Well if your answer is chlorine, you're absolutely right. Chlorine is a highly electronegative element, right? And electronegative elements, if you recall, they love electrons. In fact, we even have a scale, the Pauling scale, that measures this inherent love for electrons of different atoms. Now as you can see in the Pauling scale, non-metals like nitrogen, oxygen, chlorine, non-metals love electrons. So all of these have greater electronegativity values than carbon. While on the other hand, metals, as you know, hate electrons, they want to lose electrons. Metals have electronegativity values less than that of carbon. So out here chlorine has an electronegativity of 3.0, while carbon 2.5. So chlorine is a highly electronegative element. It's much more electronegative than this carbon atom. So the electrons in this bond are going to be more closer towards the chlorine atom rather than the carbon atom, right? So therefore, because the electrons are shifting more towards chlorine, there will be a slight negative charge on the chlorine atom. And because the electrons are shifting away from this carbon atom, it will have a slight positive charge, right? Now the story doesn't actually end here. Because this carbon is now slightly positive, so this in turn will attract the electrons in this bond slightly towards itself. So therefore, the C2 carbon atom is now also going to get a partial positive charge. And this in turn will attract some of the electrons in this bond towards itself. So even the C3 will get slightly positive and so on. So as you can see, the introduction of an electronegative element to my butane molecule actually induces a partial positive charge throughout my molecule, right? So therefore, inductive effect is nothing but the push or pull of electrons across sigma bonds. Sigma bonds basically refers to these single bonds that arises due to a difference in the electronegativities of the surrounding atoms. So therefore, whenever I have a highly electronegative element like chlorine attached to a carbon chain, then this electronegative element essentially pulls the electrons across the sigma bonds of the carbon chain towards itself, thereby inducing a partial positive charge throughout the molecule. Now the magnitude of the induced positive charge on the carbon atom will be the highest, the closer I am to chlorine as this carbon will face the full force of this electron pull. But as I keep moving further away in my carbon chain, the effective pull of the chlorine atom faced by these carbon atoms at the end will be much lower, right? So therefore, the magnitude of the induced positive charge will be the highest at the first carbon atom, so it will be the highest at the first carbon atom followed by the second carbon atom and the third carbon atom and so on, right? Now it's been found out experimentally that the magnitude of this induced positive charge actually keeps decreasing drastically the further away I move in the carbon chain. And for all practical purposes, the amount of positive charge that is developed after the third carbon has been found out to be almost non-existent. So therefore this inductive effect is actually distance dependent and it decreases rapidly the further away I move from the group causing the induction. Now one final thing that I'd like to add is that while butane is non-polar, there is no positive or negative charges in butane. But addition of a chlorine atom will instantly polarize the molecule. It will create this positive and negative charges. So the molecule will now be polarized, it will be like polar. And as long as this chlorine atom is there, the molecule will always remain polar, right? So therefore inductive effect is also a permanent effect. It creates permanent polarization in a molecule. So whenever I have something that is more electronegative than carbon attached to my carbon chain, there is going to be an electron pull from my carbon chain towards the more electronegative element, right? So this will lead to the development of some partial positive charge in my molecule. Now instead of having a more electronegative element, if I had a less electronegative element, then what do you think will happen this time? So what I have out here is sodium, sodium is a metal attached to a carbon atom. And as we have seen earlier, metals hate electrons. So in this case, the electronegativity of carbon will be much higher than that of sodium. So the electrons in this bond are going to be more towards the carbon atom rather than sodium, right? So this time there will in fact be a partial negative charge over the carbon atom and a partial positive charge over sodium, right? Now because this carbon is now slightly negative, so it's going to push this electron in this bond away from it. So this will lead to the development of some slight negative charge on the next carbon atom, which in turn will push electrons in the next bond, leading to the development of some negative charge in the next carbon atom and so on. So therefore we can say that the presence of a less electronegative element actually pushes electrons towards my carbon chain, thereby inducing a partial negative charge throughout the chain, right? Now whenever a group pulls electrons away from my carbon chain, let's consider this to be my system, then it actually reduces the electron density of the system, right? So this is what we call the minus I effect, minus as it reduces the electron density of my system. Now on the other hand, if something pushes electrons away from it, then this will increase the electron density of my system. So it will add to the electron density of the system. And this is what we call a plus I effect, plus I. So therefore inductive effect can happen both ways. It can both be minus I as well as plus I. Now one important thing that I'd like to add is that what I've drawn out here is a carbon-sodium-covalent bond, right? Now this is actually not right because metals as we know form ionic bonds rather than covalent bonds. So we won't realistically ever have a sodium covalently bonded to a butane molecule. So therefore because metals can't form covalent bonds with my carbon chain, so let's remove metals from a picture. So if there aren't metals, what are the kind of groups that can show plus I? That's a good question. Well anything that is negatively charged like say O minus, anything that is negatively charged will not pull more electrons towards itself as it will make it more negative and more unstable. Anything that is negatively charged in fact pushes electrons away from it. So these are the kind of things that show the plus I effect. Now remember that oxygen itself is electronegative. It's more electronegative than carbon but the moment I have O minus because it's already negatively charged so it doesn't want more electrons. So therefore it's love for electrons or electronegativity actually decreases. So therefore things that are negatively charged like O minus and something like NH minus, anything that is negatively charged will push electrons away from it and therefore they will act as plus I. So to summarize highly electronegative elements like our halogens which are the fluorine, chlorine, bromine and iodine, highly electronegative elements like these pull electrons towards themselves so they act as minus I while things that are negatively charged push electrons away and they act as plus I. Now besides these groups there are also various other groups that can show minus I and plus I and we're going to look into a few of these and also compare the relative strengths that is how strongly they push or pull electrons in an upcoming video.