 Hi folks, Shehzad here and today we are going to try something new. We have our very famous All of our very famous Mahesh sir out here So what I'm going to do what we are going to do is I'm going to teach him a little bit of chemistry and He's going to ask me questions. I hear that he is a chemistry noob and He's going to ask me noob questions. So let's see Anyways, we are talking about free radical reactions We talked a lot about free radical reactions and one of the most famous Free radical reactions that we have was actually discovered by this guy and It's pretty old. It's one of the oldest free radical reactions that we have. We actually discovered it in the year 1855 now as you might have guessed this reaction is called would's reaction and Would's reaction actually involves tough preparation or the formation of an alkane something like say butane butane butane from from an alkyl halide and if you have to make butane then the alkyl halide that we need to take is Has to be some propyl halide. Maybe some propyl bromide So what we need to do is we need to take some propyl bromide in the presence of some metal isn't that ethyl bromide Yeah, you are not a noob. I mean, yeah, it's it's it's ethyl bromide. Yeah, okay You're absolutely right. I was just checking, you know, if you are a noob or not So what what we do is like we take ethyl bromide in the presence of some metal like sodium And we need to take some solvents to facilitate these reactions We don't we don't we can't take water out here because sodium reacts with water sodium reacts with water to give sodium hydroxide and hydrogen So what we use instead is something that is inert something like ether some dry ether Now ether also has like ability to absorb some water molecules from From air so it has some moisture on top of it. We don't we don't want that We don't want water anywhere near this reaction because sodium is going to react with water So what we do is like we we take this and and and we get a butane one second. Why are we using sodium again? Yeah, we'll come to that why are we using sodium and we'll come to why are we like doing all these things This is the reaction that happens. You can make you can't make any alkane by the way You can only make alkanes that are symmetrical. So this is like a very big limitation of this reaction You can only make symmetrical alkane. So what are what are symmetrical alkanes? Yeah, you can you like you should take a guess. Yeah, I think symmetrical alkanes would be Where you can like sort of like draw a line in between and then the Two halves would be the mirror images of each other like butane is Yeah, yeah, you are right. Uh, what about what about propane? Do you think propane is a symmetrical alkane? um No Because I mean wherever you put a line you can divide it right out here and into two equal halves, right? But yeah on the left side i'm getting c and on the right side i'm getting h So that's not a mirror image, right? Okay, but uh, this is just a representation of an organic molecule, right? Okay, anyways, let's let's let's not go there. No, but is it is it is propane? Symmetrical You know if you if you talk about like symmetry, so that's why I felt like it's important to okay Talk about symmetry like this is actually like a propane molecule. Okay You have these h's and this h's so you actually can divide a propane molecule into two equal halves Like you can you can like pass a plane right through here and it can be divided into two equal halves Uh, but that's not what we are talking about right now So when when I said that when I say like I'm talking about a symmetrical alkane What I mean is that as you said earlier What I mean is we should like we should be able to divide it into two equal carbon chains Okay, okay two equal carbon like in in propane you can't make it into two equal carbon chains That's that's what I mean. Okay. It's not like symmetrical symmetrical. Anyways, uh, so The thing is it's even though it's very famous and it's pretty old But it's not that useful right now and we'll come we'll talk all about this One of the most important things why it's not that you're useful is like you can't make Simply anything you can only make symmetrical alkanes and and another important Issue with this reaction is that the yield of the reaction is pretty low Like you won't like if you're making butane, you won't only get butane You'll also get some other stuff and look into that also. So ultimately the The amount of butane that you'll get will be low. So it's not a very good reaction However, uh, it's still there. It's still hanging around not because it's very famous That's one of the reason but also because you can actually make it's actually a good way of making a small strained cyclic molecules like cyclopropane And cyclic butane in fact even now it's one of the best ways to make this kind of highly strained molecules And we'll talk talk more about this later on in the video. Let's look into the mechanism I think it's very important right now to go into the mechanism to understand what's really going on Okay, so what we do let me let me go down so what we do is we Say take a beaker and we cut some sodium sodium metal up and so we add some sodium metal out here and we add our we add our methyl, sorry What is it ethyl bromide, right? We add our ethyl bromide and a solvent. Okay Uh, so if we just do that like nothing much is going to happen But but if we heat this mixture up We will see like there will be like some some reaction we can understand that there will be some reaction that's going on So what happens is that uh this sodium metal? It's a metal, right? So metals do the love electrons or do the hate electrons? This is the new part of my Let's see. Um, I know metals have a lot of free electrons Um But is it like oh, I know the electronic configuration of a metal. So an is 11 Uh, so it has one extra electron and if it loses it it'll become stable. So it'll it'll like to give electron. That's my guess That that's your guess it will it will like to lose electrons, right? I like to lose electrons. Yes Yeah, so like, you know one one interesting question like So we get sodium metal, right? You have sodium metal in your lab, right? Does it just like gives out electrons just like that? Oh, no, it can't give out like just like that. Yeah, of course not and why is that like what do you think? Because if it gives a I mean there's if it gives an electron it'll have a positive charge So it'll pull it back. So you'll need I mean It it would love the octet state, but Probably in a bonded state. Yeah, you are you are like absolutely you're like absolutely, right? So if you just like add some test, uh, ethyl bromide to sodium metal nothing much is gonna happen But then if we heat it up So if we heat it up then this like, you know, we could force like some of the electrons to vibrate and move out from this sodium crystal So what's going to happen is that this this? ethyl bromides that we have They are going to like they're going to come in contact with this sodium metal, right? So they are going to like accept some of these electrons and they are going to convert into this CH3CH2 radical and we are minus Let's let's take a moment and let's let's break this down. What's happening out here? So think of it Whenever you look like whenever you look at an organic like Reaction we try to look at the electronic configuration try and understand and that gives a sense of what's going on So let's think of this bond like breaking up like this like these are single headed arrows So if it breaks up just imagine that it if if it breaks up Then I'll get a carbon radical out here and I'll get a bromine radical out here, right? Can I ask a quick question like what's our definition of a radical here? Like when do you call something a radical? We call something a radical when it has unpaired electrons Okay, cool. Make like, you know Yeah, like the easy definition would be like an unpaired electron if you don't go into like the whole Molecular orbital quantum thing. Yeah, it's an if anything has an unpaired electron. We say that it's a radical. Okay, okay So think of it like breaking down like this. So this bromine is like neutral It was neutral right in profile bromide. It's neutral. It has one electron out here So it's breaking down and it's coming here and now if it accepts another electron Then this is going to get an extra electron. So we are going to get a bromine minus Yes, yes, which we call a bromide bromide ion Now what's really driving this reaction is that once the bromide ions form So we have this n a plus and as you correctly mentioned out it won't want to like, you know It would lie off to go to its octet state But if it loses an electron it will become positively charged. It's in a very strange place, right? But the br minus like if like this whole the br minus if it gets formed it can stabilize this n a plus ions, right? So it's like awesome for both of them So so the n a br gets formed and will be left with the with this radical, right? Let me Let me quickly rub this off. So what we're going to get is we are going to get this Now, of course not a single radical is it's not that there'll be only one single radical that is going to be formed There'll be like loads of propyl molecule propyl bromide molecules come in contact. So there'll be like Some other chemicals also getting formed, right? Yeah So there'll be some more radicals that are going to get formed Now these radicals obviously as you can see this carbon like its octet is not complete, right? So so it's it's pretty reactive. So both of these radicals can then combine can then combine And this is going to form a butane molecule Uh, I can see where that symmetry thing came from now. Yeah. Yeah, exactly exactly So now now that you've figured that out like the symmetry thing Uh, let me ask you a question How like will you be able to make a propane molecule using using this reaction? I'll I'll I'll help you along the way So we have sodium. We have dry ether and I want What do I start with I think yeah, if you use A methyl bromide a combo of methyl bromide and ethyl bromide and put that Yeah, absolutely. If I make a combo of methyl bromide and ethyl bromide Okay You should get this, right? Yeah Yeah, do you see any like, you know any demerits anything To this reaction Like can you think of some demerits of this reaction of of doing it in this way? Um, yeah, yeah, uh We will also get a lot of unwanted products will get butanes anything. Yeah, because this this methyl radical can react with another Methyl radical, right? It's not going to wait and be like, hey, you are like ethyl and I'm going to react with you Yes, okay. It's it's going to be like it's it's going to give you loads of stuff It it can also give you this and it can also give like even this ethyl radicals can react with other ethyl radicals So you're going to get loads of other products, right? Uh, so the first thing is your yield is going to be low Like because there's so many unwanted stuff you're getting. Yes Yeah, yeah, your yield is going to be low. Maybe you'll you'll get like, I don't know 10% 20% maybe And more importantly, uh, you see this this this lk's that are getting formed. They are like pretty similar, right? They're like different by only one or two carbon atoms. Hmm, right Uh, so what's going to happen is this they are going to have like pretty much similar physical and chemical properties, right? Uh, I see where you're going with this Yeah, so it's going to be very difficult to even separate them You get it, right? Right. So when it comes to a mixture of alkanes, it's like wood's reaction is like a Not good enough Okay Now now you might think you might think uh that hey, there's no issues when it comes to making butane, right? When it comes to making Symmetrical alkanes it should be like super awesome and everything and everything should be like a really good And really happy, right? Yeah, but it turns out that even there there's a problem Okay, let's see. Whatever. Let's see. Let's let let's see you like what's what's going on Oh my god. I'm I'm like done with my sketchbook file Okay, so let's start this is this is fun. We should do this more often Okay, anyways anyways anyways, uh, so we have we have an ethyl radical, right? In fact, like let me go ahead and let me like draw it Like chemists generally don't like to take we are very lazy people, right? So we don't want to draw all this stuff anyways Anyways, another thing that's going to happen that can happen is this Look at this like carefully Now it's not necessary for this radical to come and collide against this radical head on, right? Like many a time it will be like colliding against this hydrogen atom In fact, like the probability of it like colliding against this hydrogen is going to be appreciably high because there are so many hydrogen atoms, right? And only one One carbon radical So one of the other things that can happen is that it can actually abstract this hydrogen from from this radical So let's see what happens. So imagine this bond breaking breaking down like this Okay, so if we can imagine that so what will I have I'll have I'll have I'll have an electron out here an electron out here, right? So now these two can combine and these two can combine Right. Oh, I get it. You have an ethane and an ethene Yes, you have an ethane like, you know, like simply we say that this radical can abstract a hydrogen And if it abstracts a hydrogen you're going to get this and the radical left out here and both of this can combine And you can get anything So once more like even even if you start from a Oh my god from from a Okay, okay. Yeah, even if you start from from from this, it's we are going to get some more extra products. Okay. In fact It's still tolerable when it comes to like first degree radicals, but if we take a say second degree or third degree radical, let's let's say We take something like Let's let's Let's say I want to make this molecule I want to make this Now this This is a symmetrical like let's let's let's ask that question again, right? Symmetry like yeah, do you think it's symmetrical? Yeah, so we can we can break this into two. So how how what would you do like? like it's a symmetrical alkane and I want to Make what do you start where do you start from? So I start with What do you call that isobutyl bromide? Is that what you call it? Yeah, whatever. Let's not fix it on names. Okay. Uh, like we'll get this. Okay, this right Yes, now what's going to happen the radical that is going to form It's going to form this radical, right? Yes pretty crowded radical, right? And like, you know when when When this wants to come and collide against another of this radical They're they're going to like hinder each other, right? There's they're going to like for this carbon radicals to come pretty close These two will like start hindering each other So the probability of this radical going ahead and Of we call this a third degree radical going ahead and colliding against another third degree radical to form Like this bond is actually going to be much lower compared to a third degree radical colliding against these hydrogen atoms, right? Right right So like, you know, it's not only like Symmetrical alkanes you can make symmetrical alkanes, but if your starting point is like, you know Second degree or third degree alkyl halides, then the yield is going to be even lower. Got it Mainly because there are so many more hydrogen atoms To collide. Yeah, mainly because there are like so many more hydrogen atoms that can collide against and also because It's actually going to be difficult for both of these two. Oh, yeah Oh, that's like a double gamma and they're they're going to hit. Yeah, it's like It has like loads of baggage along with it Right. Yeah So the point is Wood's reaction is like a Yeah, why are we learning about it? But but 1855 dude like 1855 But so we should give credit I'm sure there's so many other things That are obsolete today and we don't learn that's that's a very good question Like that's a very good question because like, you know, interestingly We actually don't need to prepare alkanes In the lab because most of them are commercially available Petroleum products, they're alkanes, right? This whole industry like every single product that we're using nowadays like they are Some of these alkanes like you put stuff on the alkanes. They're like the starting material Of everything and you actually don't need to prepare them. We get them naturally We get them through like, you know cracking of bigger alkanes and breaking them down and everything So they're like petroleum products So not much of a laboratory usage to prepare alkanes because we just get them But yeah, wood's reaction. Let's come to this point. Yeah, this this is the most Interesting bit of woods Right now. Uh, I am like, you know, like everybody else who is listening to this video. Please don't judge me Uh, it's a wonderful reaction and you should like Read this read up on this reaction anyways, uh coming back so Before we go there like let me give you an interesting. Let me ask you an interesting question. What if I have this Uh, what if I have instead of having one bromine attached out here? What if I take two bromine? What what do you think is going to happen and and and I do sodium in tri ether What are the products do you think we'll get? Okay, I mean first of all, that should be a ch2, right? Like on the end left side not a ch3 anyways nitpicking, but let's see what we get attention to details, yeah um What will we get two radicals now? um And uh, oh, okay. Okay. Okay. And those two We'll try to form a bond and that's how you get a cyclo stuff. Is that? Yeah, yeah, exactly those two will try to form a bond and you'll get a cyclic stuff You will also get other products exactly you may also get linear products. Um, I can imagine you might get linear products and one like, you know I don't think so it like specifically you can get linear products You won't be like absolutely wrong, but a more obvious answer would be this right? Oh, yeah Yeah Right linear like if you want to get a linear product you need to There are two radicals on two ends right? Yeah, all of them need to be hydrogen abstraction from somewhere You need a hydrogen abstraction from somewhere that that might also happen. So one two three four five six You can you can also get this Okay, but let's not focus on that. This is like a six-membered ring, which is like really stable and all What happened is like what happens is that in a three-membered ring there is loads of loads of strain in the molecule like There's loads of strain Are you are you like aware of these kind of strains? No, no, I don't know Okay, so so like if you look out here this carbon has two hydrants. It's it has four bonds, right? Like like like think about a methane molecule Methane molecule has four hydrogens This has like this also has four bonds. They're not four single bonds. This also has four single bonds. They're not hydrogen But it's okay uh, if you if you recollect A ch4 molecule actually is tetrahedral, right? Yes, this is like the actual shape of a ch4 molecule So this this is because like, you know, if we have four bonds then This bond angle is like 109.5 degrees, which is much better than this 90 degrees Like you are just talking thinking about it two-dimensionally, right? So two dimensionally putting these electron clouds at 90 degrees seems the best arrangement But three dimensionally this electric putting this electron clouds at 109.5 degrees is like the best Possible arrangement for a carbon having four bonds around it But this does not have that like, you know, it's it's forced into these 60 degree bonds out here Okay, so what happens is like this this this is this actually breaks apart You know, it's very easy for this to actually break And like, you know form form a radical out here or something In fact, like this this cyclopropane molecules are like very reactive and then in fact react like alkene So we'll talk about alkene some other day But the point is they are strained Okay, uh, so Chemically it turns out that there are very few other reactions that you can do to actually make cyclopropane because it's a very Very strained product But wood's reaction turns out even even though you might get like poor yields But wood's reaction turns out. It's like one of the easiest ways to prepare cyclopropane So Right now what I see is like, you know, the best the the most important thing of woods is like doing this kind of stuff Okay, and then do we still use today to woods reaction for cyclopsychloalkenes? Yeah, yeah, I think I think we do that. I I just Uh, so a guy like making cyclopropane. Oh Uh on youtube the other day and it was fun. Like just seeing seeing it was fun Yeah, okay Yeah, so that brings to the end, um Of of this video Got it