 Okay, so we discussed with alkene preparation and its chemical properties. Next the second part of the chapter we have that is alkene, okay, so write down the heading. General formula of alkene is CNH2N, with this formula, if you find out degree of unsaturation, you'll get it as one, okay. The various preparation methods write down method of preparation of alkene. See alkene can be prepared by from alkyl halide by elimination reaction, okay. Alkene can be prepared by alkyl halide by elimination reaction. What is elimination reaction? We'll see. Write down the first point here, first method from alkyl halide. What happens in this? Suppose you have an alkyl halide R, CH2, CH2X, like this. When it is heated with alkoholic KOH, it's KOH in presence of alcohol, right, if you heat this. Then the product in this reaction would be CH double bond CH2, okay, this is the product we get. How this reaction happens, you see, you have alkoholic KOH, means you are taking an alcohol, for example, C2H5OH and the base KOH. Alcohol has acetic hydrogen here, you see, H plus here, this is OH minus, H plus OH minus forms H2O and we get a salt of it, C2H5OH minus and K plus, salt. This salt, what it does, it takes beta hydrogen from the molecule. This molecule, you see, the carbon which has this halogen present, this is alpha carbon and this carbon is beta carbon, then gamma, delta, like that we go. Alpha carbon is a carbon atom which attached with the halogen atom, correct. So the base we have, C2H5O minus, it takes hydrogen from the beta carbon forms C2H5OH, C2H5OH, okay. Then this sigma comes here, makes a pi and this halogen atom goes out as a leaving group. So we get here our CH double bond CH2, this X minus combines with K plus forms KX, this is the product we get. This reaction is a type of elimination reaction, right, so preparation of alkene from alkyl halide is done by elimination reaction. Elimination reaction, we have different, different types, E1, E2, E1, CB, briefly I will discuss what is E1, E2 over here, in detail we will again see in reaction mechanism, okay. So write down the point here, alkene can be prepared by alkyl halide, alkene can be prepared by alkyl halide from elimination through elimination reaction, through elimination reaction, okay. So elimination reaction you see, two different types we are going to discuss here, first of all we have E1 and then second we have E2, E1 like we have SN1, E2 like we have SN2, similar to that, okay. What happens in E1 mechanism you see, rate of E1 reaction would be maximum in tertiary alkyl halide, then secondary and then one degree, this is the order of reactivity for alkyl halide. So suppose we have a tertiary alkyl halide for example CCl, then we have CH3, CH2, one more hydrogen we have here and here we have CH3, tertiary alkyl halide, tertiary alkyl halide in presence of, in tertiary alkyl halide what happens, if you heat this reaction molecule simply, then this halogen atom comes out easily as a leaving group and forms a carbocation here. So we get here HCH2, CCH3, CH3 positive charge and Cl minus goes out on heating. So you will get a carbocation here in between. And then from the beta carbon, hydrogen comes out as H plus leaving this electron pair behind. So we will get a double bond here and this is the alkene. H plus comes out which combines with Cl, forms HCl, this is E1 mechanism. If you have E2 mechanism then what happens you see, consider this molecule, carbon has a leaving group Cl, one hydrogen here. Hydrogen must be required at beta carbon for elimination reaction. In presence of a base, suppose OH minus I am taking as a base. So what happens, this OH minus takes this H plus, the reaction would be slow here. And when this H plus comes out, we will get a transition state over here. Okay, what is the transition state? T, C, this hydrogen is getting attached with OH, this carbon-carbon bond is about to form and this Cl-carbon-chlorine bond is about to break. This is the transition state we have. Means what? TS transition state. Means what? This bond is about to form, this bond is about to break, this bond is about to form and this bond is about to break. It is a situation where exactly the OH H bond is about to form, carbon-chlorine bond is about to break and carbon-carbon bond is about to form. This happens in between and then this finally converts into an alkene and H2O forms and Cl- also goes out. This happens in one step. It is a single step reaction we have in order to understand, we write it this way, but it happens in one step. You can simply understand it this way. Base takes this H plus, this sigma bond forms a pi here and chlorine takes the sigma bond and goes out as a living and we get a double bond here. Now you look at this example in this. Suppose we have a molecule CS3, CH2, CHX and CH3, CS3 I will write down this way. When it is heated with alkoholic KOH then what happens? One possibility is what? One possibility is this HNX combines and forms HX figure double bond here. The product would be this, one of the product in this, CH double bond CHCH2. This is one possibility. Another possibility is what? That this X combines with this hydrogen on the right and forms a double bond over here. That would be CH3, CH2, CH double bond CH2, the two different alkenes we are getting here. Right? So the alkene which is more stable is a major product here. So in this case we can talk about major or minor product, okay? So which one is more stable in this two alkene? Left one or the right one? How do we check the stability of an alkene? Stability of an alkene, how do we check? Hyperconjugation. For hyperconjugation, what we check? For hyperconjugation, what we check? Alpha hydrogen, isn't it? Yes. Which one, like in this molecule, how many alpha hydrogen we have? What is the alpha hydrogen here? Could you tell me? This is CS3. This is CS3. How many alpha hydrogen we have on the left side? Yes, we have six here and we have five here. Is it five? No, we have only two. Only this one is alpha carbon. So we have two alpha hydrogen here. So obviously the first one has more alpha hydrogen. So it is more stable, correct? And the more stable product, we call it as sedgef product, sedgef product. And the minor one is the Hoffman product, Hoffman product. So this product, the one which is more stable is major, forms more and this one is minor, forms less. Okay. We can also prepare alcohol from dihalytes. Second one. Halides we have seen from dihalytes. Dihalytes we have of two types. One is gem dihalytes and other one is visceral. Have you heard these names? Visceral dihalytes. What is gem dihalytes in which one carbon contains both halogen or right on this way? Both halogen atom because it is dihalytes, so we have two halogen atoms. So both halogen atoms attached to the same carbon atom. For example, if you write down RCHX2 like this, this is a gem dihalytes because both halogen at the same carbon. On the other hand, visceral dihalytes is the one in which two halogen atom attached at the adjacent carbon atom, adjacent carbon atom. For example, RCHCHCH3, here we have X, here we have X. This is visceral dihalytes. If they are not at the adjacent carbon, then we can say one three dihalytes or something like that. Like, suppose if you have a molecule this way, CH2, CH2, CH2, here we have X, here we have X. So it is one comma three dihalytes. We don't have such name. Okay. Yeah. Now you look at the reaction here. If you have gem dihalytes, then what happens? You see. Write down gem dihalytes when heated with Na in presence of ether, gem dihalytes when heated with Na in presence of ether, Na in presence of ether, forms higher alkene, forms higher alkene. For example, you see RCHX2 with Na2 Na, two of this we are taking, heated. It forms RCH, double bond CHR plus 2 NaX, kind of woods reaction, as you can understand. No, no, dialgene won't form. This two halogen will go out. We have a double bond here from the other molecule. This will get attached to the double bond with the other molecule of the carbon atom. Okay. If you take two different alkyl halide here, dialkyl halide here, then we'll get three different types of alkene. All possibility we have that will come mine. Okay. So remember in this we are getting higher alkene, higher alkene. Next slide down. Visceral dihalytes, when visceral dihalytes is heated with zinc dust, zinc dust, then it forms alkene, then it forms alkene with same number of carbon atom, with same number of carbon atom. Okay. For example, you see we have RCHCHRXX zinc dust we are using, fine powder of zinc we are using to increase the surface area so that we can have better interaction. We are heating it around 300 degrees Celsius. It forms ZnCl2 and we get RCH double bond CHR, this is the product we get. One point you note here, if you have one three dihalytes like this you see CH2, CH2, CH2X. If this is heated with zinc dust, then we don't get here alkene, but we get cyclopropane. This will go out, we get a radical here, we get a radical here, these two combines and forms cyclopropane. However, the product is not that stable. Okay. Next. Right on next, from alcohol, right on alcohol is heated in presence of an acid alcohol when heated in presence of an acid, alcohol when heated in presence of an acid goes under dehydration, goes under dehydration and forms alkene and forms alkene. This we call it as dehydration reaction or dehydration of alcohol, dehydration of alcohol. What is dehydration? Dehydration is removal of water molecule, removal of H2O. Okay. So, in this what happens here, we have RCHCHCH2OH. This is the alcohol we have, suppose. When you heat this with acid around 160 or 170 degree Celsius roughly we heat. Generally elimination takes place at higher temperature, right 160 degree Celsius we heat. Then what happens first of all, this acid will give H+, and with this H+, this OH gets protonates. Means it takes H+, from this acid, this H+, will get absorbed by this OH here. So, what we get you see, we get RCHCHCH2OH2 and positive charge on oxygen like this, correct. Now oxygen is an electronegative element, positive charge on oxygen is not stable, correct. So, this will take the electron pair, oxygen will drag the electron pair and goes out as water molecule and forms a carbocation, CH2 positive charge. So, for this reaction first of all, the intermediate is a carbocation, intermediate is a carbocation. When carbocation is an intermediate, stability of carbocation also will see by rearrangement. So, rearrangement of carbocation possible, rearrangement possible, okay. Rearrangement in order to get more stable carbocation, right. How it happens, everything will discuss in detail later. But this is just an idea you must have, okay. So, here rearrangement is not possible, further when you heat this then H+, comes out from the adjacent carbon leaving this electron pair behind and we get RCH2, double bond CH2, right. So, H+, that consumes in the first step releases in the last step here, right, plus H+. So hence, there is no net consumption of H+, here and we say acid is behaving as a catalyst. Acid is behaving as a catalyst, as a catalyst and hence this reaction is also called as acid catalyzed reaction, right. This reaction is also known as acid catalyzed reaction, okay CH, okay. Since acid is behaving as a catalyst, so acid catalyzed reaction, right. Obviously, when alkene is forming, then major product is always more stable alkene. Now, actually see what happens, OH is a poor living group, correct. OH is a poor living group. If you want to remove this OH, then you have to protonate it. Without protonation, you cannot remove OH from here. So, the lone pair of oxygen, we have two lone pair, electron density is high. So, an acid gives H+, so H+, automatically attracts towards the electron pair or, you know, the electron cloud of oxygen atom over there and it gets trapped on the oxygen atom forms this. Once it forms, it feels like, okay, this positive charge is not stable, right. It is not stable because of the positive charge. Then this takes this electron pair from the carbon atom and goes out. So, it takes the electron pair, electron of carbon as well. That's why carbon gets positive charge on it and that is how the carbocation forms in this reaction. Understood? For alcohol, you must keep this reaction in mind. Always, OH in alcohol is a very poor living group. It won't go out as OH-, never. If you want to remove OH, you have to protonate it. So, in presence of acid, OH gets protonates from forms OH2+, and then H2 can eliminate easily because H2O is a better living group than OH. Understood? Okay, now you see this question and tell me what product you get if the question is this. We have CH3, CH, CH3, CH, CH3, OH, heating in presence of acid. Tell me the product in this one. Tell me the product in this. Yes, so what is the product you got? 2-methyl but 2-in. Okay, okay, see. See, first of all, what happens in this reaction? This acid will give H+, and this H+, with this H+, this OH will protonate, right? We'll get H2O+, then H2O goes out, we'll get a positive charge here on this carbon atom. So, carbocation that we get in the first step is CH3, CH, CH3, CH3, CH positive charge, CH3, this is the carbocation we get. Now, this carbocation can rearrange in order to get more stable carbocation. What is the alpha hydrogen we have here for this carbocation? Could you tell me the number of alpha hydrogen? 4, right? Now, suppose in order to get more stable carbocation, what happens? This hydrogen takes this electron pair and rearranged itself onto this carbon atom, right? Next carbon atom. This we call it as 1,2 hydride shift, because hydrogen is shifting, 1,2 hydride shift, correct? So, this would be CH3, C double bond, CH, sorry, not double bond. CS3 single bond C, CH, and this one edge from the adjacent carbon, CH3, CH3 here, and a positive charge on carbon atom. So, what is the number of alpha hydrogen for this carbocation? Number of alpha hydrogen here, 8, right? 8 alpha hydrogen, alpha carbon, alpha carbon, alpha carbon, 3 plus 3 plus 2, 8, right? So, obviously, more alpha hydrogen, more stable the carbocation is. Hence, this carbocation is more stable than this one. This we call it as 1,2 hydride shift. With this shifting, the carbocation becomes more stable. Hence, we have to consider this shifting here, right? Once this happens, right? Then we can have hydrogen we can remove from any one of the carbon atom, because adjacent one is this, or this, or this, anyway. So, two products possible here, two products possible here. One is when hydrogen comes out from this carbon atom, it is CH2 double bond, CCH3, CH2, CH3. And another one is CH3, C double bond CH, CH3, CH3. Tell me which one is more stable, which alkene. Second one or the first one? Yeah, this is major, because it is more stable, so it is major. No, not the first one. See, number of alpha hydrogen you count here. Alkene, number of alpha hydrogen you count. How many alpha hydrogen we have here? You have 3 plus 2, 5 alpha hydrogen. But for this one, it is 3 plus 3 plus 3, 9 alpha hydrogen. So, this one is more stable than this one. This we call it as, again, set Jeff product. And the other one is Hoffman. Okay, so this kind of shifting you must consider whenever carbocation forms. We call it as rearrangement of carbocation. So, whether you do it or not in the reaction, the reactant itself will do on its own. Right? So, whenever it is possible, we always have the rearrangement. Rearrangement is possible in the reaction in which the carbocation forms. Okay? Since hydrogen is shifting here, it is hydride shift. Imagine, if we would have here CS3, one more CS3 present in this case. Then one more methyl can shift. Then it would be 1-2 methyl shift. If it is phenyl, then 1-2 phenyl shift. So, depending upon the group, we can have the name of the shifting. Correct? Objective is to get more stable carbocation. After this, also, if the shifting is possible and we are getting more stable carbocation, then we'll do the shifting again. So, we keep on doing the shifting till we get more stable carbocation. Okay? Always from less to more stable carbocation forms. More to less, not possible. Understood? No doubt? Yeah. Next reaction we have. By coal-based synthesis, similar kind of reaction. Synthesis, electrolysis. What happens in this reaction, you see? Suppose we have CS3 C double bond O, K plus, which is CH2. And then one more, we have CH2 C double bond O, O minus K plus. Okay? This forms an ion when K plus goes out, plus 2K plus. Now from this, oxygen releases two electron and we get a radical over here. Goes this way. CH2 C double bond O, oxygen radical. CH2 C double bond O, oxygen radical plus 2 electron. You see, O negative charge means what? This negative charge we have on oxygen means oxygen has six electron here. And hence a negative charge, like this. And hence a negative charge, right? So it releases two electron, one from here, one from here. So we get two radical here, odd electrons here. And then from this, what happens, there is homolysis between carbon, between CS2 and the carbonyl group, COO group. So in homolysis, what happens, one of the bond here, one of the electron is taken up this carbon and another one is taken up this carbon. Same thing happens over here. So we get here CH2, CH2 radical on this and on this. Plus we'll get two molecules of CO2. And then these two radical combines and forms CH2, CH2. This is how alkene forms in this reaction. See in this one, it is an ion, right? Four carbon atom we have, we call it as succinate ion. If you have CH2 C double bond OOH, CH2 C double bond OOH, that is succinic acid. It is a salt of succinic acid, basically. What I'm telling you, if you just place hydrogen over here and hydrogen over here, no charge, it is succinic acid. Salt of succinic acid, this one is potassium salt of succinic acid, clear? So it is succinate ion, potassium salt of succinic acid. This is the reaction of anode, okay? It happens like this radical has, this is the radical we are getting. And free radical has this property that it eliminates a neutral molecule in order to get a new radical. So from this radical, two CO2 has been eliminated, so that we'll get a new radical here, and it happens on its own again. This two radical again combines and forms alkene, because radicals are highly reactive. On adjacent carbon, if radical forms, both combines and forms a bi-bond there. This is the reaction at anode, again you see, CO2 evolves at anode here. It's the same thing like we did in the alkene. Similarly, you can write down the reaction at cathode as well, you see. For cathode, what happens? 2k plus plus 2 electron gives 2k. And when it dissolves in H2O, it forms 2k OH plus H2O. You can also write down here, 2k plus plus H2O plus 2 electron gives this. Yes, it was an anodic reaction. Here you see, at cathode, hydrogen gas evolves. At anode, CO2 evolves, at cathode, H2 evolves. Another reaction we have, Wittig reaction. Wittig reaction. It is the preparation reaction of alkene, preparation method. It is the preparation method of alkene from carbonyl compound. Carbonyl compound means aldehyde or ketone. Preparation reaction of alkene from carbonyl compound, aldehyde and ketone. Okay. So in this, we use Wittig reagent. What is Wittig reagent? I'll tell you. Wittig reagent is triphenyl phosphorane, triphenyl ph3. This is triphenyl, then phosphorous, then double bond. You can take CH2 here or instead of CH2, 2 alkyl group also you can take. It means anyone you can take if you want. Ph3P double bond C, R, R, R dash, anything you can take. Right. This is triphenyl phosphorane. Name if you want to write down. Phenyl is the benzene ring. So if you have any aldehyde or ketone, for example, we have this reaction Ph3P double bond CH2. And this reacts with R, C double bond OH. It forms what? What you need to do just to see this. C double bond O and P double bond CH2. So this double bond CH2 and double bond O, you just interchange. Okay. Double bond CH2 and double bond O, you just interchange. What we get? Ph3 whole thrice P double bond O will have over here and RC double bond CH2H. This is the alkene we get. This reaction is there in aldehyde ketone chapter also. There we can discuss the mechanism. But how to write down the product? Double bond O and double bond CH2, you have to interchange. This we call this is Wittig reaction. Wittig reagent is triphenyl phosphoryl. Important reaction. Yeah. Tell me. Any doubt? Next, preparation is done. Write down the properties, physical properties. First one, the physical state C2 to C4 carbon atom. Means the molecule in which 2 to 4 carbon atoms are present. It is colorless, orderless gas. Physical state is this. C5 to 17, it is liquid. It is colorless liquid. And C18 onwards, these are solids. Solids. This is a physical state. Okay. Alkenes cannot form hydrogen bonding with water. Edge bonding with water. Hence insoluble in water. Insoluble in water. As branching increases, same logic we have. Like we had for alkene. As branching increases. Boiling point and melting point decreases for alkenes. Melting point of cis isomer is less than to that of trans. The reason is same. Like trans we have better packing. And hence more melting point. Boiling point, if you see. Boiling point depends upon dipole moment. And dipole moments we check which one has the more dipole moment. Accordingly boiling point we can say. So we can also write. Boiling point. Is directly proportional to dipole moment. We have done this in isomerism also. Geometrical isomerism properties. These are a few chemical physical properties we have that we must remember. Next slide down. Chemical properties. First one. Hydrogenation of alkene. We have discussed this. I'll just write down. In preparation of alkene. Yes. I have told you that. The one we are doing over here in preparation of alkene that will come in the chemical properties of alkene or aldehyde ketone. So what happens in this we know already. R. CH. Double bond. CHR. We'll do the hydrogenation of this H2. In presence of catalyst any catalyst we can use nickel platinum palladium. It is an addition and it gives our CH2. CH2. Okay, we have already discussed it. Similarly you see in preparation of alkene we have discussed hydroboration reduction reaction that is also chemical reaction of this. Second reaction write down. Hello generation of alkene. Hello generation of alkene. The reaction is. RCH. Double bond. CH2. This is an alkene. With X2. Hello generation. And it is done in an. Non-polar solvent CCL4. CCL4 is a non-polar solvent. Write down. Non-polar solvent. Okay. So what happens. Both halogen atom. Get attached to the double bonded carbon atom like this. Here it is anti-addition. This is anti-addition. One halogen. I'll write down that for you. One halogen attached from the below of the carbon atom other one from the top. Like this. It is anti-addition of halogen. Order of reactivity of halogen you see it is maximum for fluorine. Then chlorine. Then bromine. And then iodine. Order of reactivity is this. Okay. See how this reaction takes place actually. Why it is anti you try to understand. Syn of hydrogenation we understood. Exoption takes place and then it has to attach from the same side. Correct. Yeah one sec. Yeah. Okay. Now you try to understand this here. We have this halogen alkene right. And we are doing bromination of it. So we have this B R B R we have. I see B R we have a non-polar molecule and solvent is also non-polar. When the solvent is non-polar so it cannot polarize this B R 2 molecule. Polarize means what? If it can polarize then it will convert into B R plus and B R minus. This conversion is not happening actually because of non-polar solvent. Okay. Because of non-polar solvent this conversion is not possible. Hence what happens? We'll have this as delta positive delta negative charge. So this positive charge will attack by this electron cloud, pi electron cloud of halogen of alkene. Right. And B R B R bond won't break over here. What happens when this attack? So we'll have this one here. Carbon, carbon bond and this carbon will attach with bromine. Dotted bond will have here just a second like this B R B R. We have delta positive here. And then this attached with this bromine. We have delta negative here like this. It happens. This is a transition state. Okay. In between it forms. This we call it as cyclic. Since bromine is there. So bromonium ion. If it is any, in general, if you say it is halonium ion. Okay. Cyclic bromonium ion forms. Slowly what happens first this forms. Then this bromine comes out as B R minus from this. Then we get here C B R C. And this two bond will be as it is here. We have the positive charge on bromine. Since the B R minus will go out. So we'll have here the positive chart and this bond would be as it is. Now in the next step, the B R minus, but that, you know, that is that has come out here. This again will attack on one of the carbon. This attacks over here. And this goes out. Since it's a cyclic ring. So it cannot attack from the same site. So it will attack from the backside so that the ring opens up. Okay. So hence what happens this bromine will come on this carbon atom on the top and the bromine, which attacks, it will come from the bottom. And hence it is the anti addition. So anti addition because of the cyclic ring forms during the react in the process of a reaction. Correct. Understood guys. Okay. Fine. So this you just remember it is not important. You have to keep this in mind. Hallogenation of alkene is anti addition. That is what you have to keep in mind. Okay. For the next class, most probably we'll have it on Friday only. I'm not very much sure. Okay. We'll let you know one day before. Okay. We'll start from this and we'll start with the reaction of hydro halogenation. Write down. Reaction with ethics. Heading you right down and just you will finish this from will start this from this in the next class. Reaction with ethics. We'll start from here. Next class will finish this. Okay. Fine. Thank you guys. Take care. Bye bye.