 Now one of the most important things that we first need to understand before we can dive into organic chemistry and organic reactions are the various electronic effects that are present within an organic molecule. Now these electronic effects basically refers to the push or pull of electron density within a particular area of an organic molecule and the most important of these electronic effects are actually the inductive effect, inductive effect and something called hyper conjugation, hyper conjugation and something that I am sure you must have come across earlier something called resonance. Now before we talk about each of these effects and what they actually mean, I first want us to take a moment and try and understand why we really need to care about these electronic effects in the first place. Let's see. So what I have out here is the hydrolysis reaction of a few alkyl halides. An alkyl halide is nothing but a hydrocarbon to which I have a halogen attached. Now if I add water to an alkyl halide, so let's consider this to be the hydrocarbon part and let's say we have a halogen X. This X can be fluorine, chlorine, bromine or iodine. And now if I add water to this, I am going to get ROH which is nothing but an alcohol and I will be left with an HX molecule. So what I have out here are actually different alkyl bromides that react with water to give me alcohol and HBR. Now the first alkyl halide is what we call a third degree alkyl halide because the carbon atom to which this halogen is attached is actually a third degree carbon atom as it is attached to three other carbon atoms. So we call this a third degree alkyl halide while this is a second degree alkyl halide and this is what we call a first degree or a primary alkyl halide. Now it turns out that this hydrolysis reaction of a third degree alkyl halide is much much faster. In fact it's almost 10 to the power 6 times faster compared to a first degree alkyl halide. So why does this happen? Now this chemical reaction that you see out here, this reaction like most chemical reactions actually happens over multiple steps. Now in the first step this halogen atom which is a highly electronegative element, electronegative elements if you recall love electrons. So this bromine atom it pulls the electrons in this bond towards itself. So in step one this alkyl halide actually breaks down into what we call a carbocation and BR minus. The water molecules then attack this carbocation to form ROH2 plus and in the final step the bromide ion that is formed abstracts a hydrogen to form the alcohol and HBr. Now these steps are not something that I simply made up. This is actually an experimentally determined fact and chemists actually came up with really clever ways to actually confirm that these really are the steps that are happening and all these steps taken together is what we call the reaction mechanism for this particular reaction. Now if we add all these steps together we should get our overall reaction. Now as you can see during the course of this reaction the carbocation as well as the ROH2 plus these are actually not a part of the overall equation but these are in fact formed over the course of the reaction right? So because these are formed in the intermediate steps these are what we call the reaction intermediates. The reaction intermediates. Now for this particular reaction this step the formation of the carbocation is actually the slowest step while all these happen really fast. So the rate of this reaction is actually depended upon how easily the reaction intermediate which in this case is the carbocation can be formed right? If the carbocation can get formed easily then the rate of the reaction will be higher but if it doesn't form that easily then the reaction will be pretty slow. Let us now take a moment and see how the carbocation gets formed in this reaction. So we have our alkyl halide in which there is a carbon bromine bond and we know that bromine is a more electro negative element. So the electrons out here in this bond are essentially much closer to bromine compared to the carbon of the hydrocarbon. So there is going to be some partial negative charge that is going to be developed over bromine while there is going to be some partial positive on the carbon atom right? Now chemical bonds are actually not static they keep on vibrating so you can think of this bond vibrating like a spring. So as this bond vibrates the bromine atom gets further away from this carbon atom and because the electrons are more closer towards bromine so they get further away from this carbon atom and so the carbon becomes more positively charged. Now during the course of this vibration if the bromine atom moves far enough then we can get our fully formed carbocation and the bromide ion. Now do remember that because this is positively charged and this is negatively charged there is going to be an electrostatic attraction that's happening out here. So these ions do not totally break apart but the bond actually keeps vibrating. Now it turns out that whenever we have a third degree alkyl halide as this bond vibrates and breaks down it turns out that these methyl groups that we have attached out here these methyl groups actually have the ability to donate electrons to push electrons towards the carbocation by an effect known as hyper conjugation. So this is one of the electronic effects that we talked about earlier and we don't really need to understand right now how this is actually happening. For the moment just remember that whenever we have alkyl groups attached to a carbocation these alkyl groups can actually donate electrons to this carbocation that is getting formed. So what happens now is that this carbocation gets relatively stabilized. So this gets relatively stabilized and the positive charge on the carbocation will actually decrease. So now there is going to be lesser of an electrostatic attraction between these two ions and it turns out that this kind of third degree alkyl halides can actually form this kind of carbocation relatively easily. Now instead of starting with a third degree alkyl halide if I say start with a first degree alkyl halide in this case because there is only one methyl group that is attached to this carbocation. So therefore in this case the carbocation doesn't get as stabilized as this third degree carbocation. So out here this carbocation is not so stabilized, not so stabilized because there is only one alkyl group that is attached. So this bond cannot actually totally break apart. So therefore it's really difficult to form a carbocation from a first degree alkyl halide. Thus when we have a third degree alkyl halide the rate of the reaction is far greater. The reaction is much faster as it is much easier to form the carbocation compared to a primary alkyl halide. So therefore whenever a chemical reaction takes place more often than not we have these reaction intermediates that get formed and the stability of these reaction intermediates can actually determine the kind of products that we can get. Now over the course of learning organic chemistry we'll encounter many such reaction intermediates. In fact we saw one today we talked about what we call the carbocation reaction intermediate. The carbocation is carbon with a positive charge but we can also have carbon anion as my reaction intermediate. Carbon anion is actually a carbon with a negative charge or we can also have something called free radicals. So we can also have a carbon free radical which is nothing but a carbon with actually an unpaired electron. So we can also have carbon free radicals as our reaction intermediates. Now coming back we have seen how the stability of these reaction intermediates plays a very crucial role in determining whether we can get a particular product or not. So one of the most fundamental things that we'll focus on in this series of videos is actually understanding the various electronic effects that can stabilize or maybe even destabilize a reaction intermediate. Now besides the stability of reaction intermediates these electronic effects are actually also responsible for the various physical and chemical properties of an organic molecule. Things like the boiling point of different molecules, their acidic or basic strength that is how easily they can accept or lose an H+. Even things like bond dissociation energy, how easily a bond can break, all of these and many more can actually be understood if we can figure out the underlying electronic effects that are present within the molecule.