Introduction to Hydrocarbons and Alkanes

Hey all, welcome to Homeschool. Hope everybody are doing good. And I am with Class 11 Chemistry. The chapter is Hydrocarbons. Hydrocarbons is one of the most important chapters in case of organic chemistry. In my previous videos, I discussed every aspects of basic organic chemistry, isn't it? We discussed how to name organic compounds, different organic compounds having different functional groups, about their naming, about their classification and we had seen very very basic aspects of organic reactions. So how they react, what way they react and what are the different electronic effects that we observe in organic compound. So everything we discussed in a detailed way and coming to this chapter. this is just the continuation of organic chemistry where you are going to study about the chemistry of the most important and basic organic compounds so here we will try to understand how a class of alkanes can be prepared and how they react okay so we know what was alkanes we studied in the previous chapter Alkanes are nothing but single bond containing organic compounds. They do not contain any functional group. You just observe carbon and hydrogen. So after all, that is what the definition of hydrocarbons is, isn't it? So hydrocarbons are. the organic compounds which have only carbon and hydrogen you will not find any functional group isn't it so we are going to study the detailed aspects of such hydrocarbons so what are the different hydrocarbons that you can observe first variety is alkane second variety is alkenes isn't it so alkenes you will observe double bonds between carbon atoms. And the third type of hydrocarbon is alkynes. So in case of alkynes, you will observe triple bond between carbon atoms, isn't it? And the fourth type of hydrocarbon, the most important variety that is aromatic hydrocarbon. So about these organic compounds you are going to study in a chapter. So what do we study about them? We just study about the basic introduction. So we'll try to understand how these things can be reactive, whether they can be reactive or not, if reactive, what way they react. you know, all of them. And then we will study about their nomenclature and then certain aspects of isomerism. Then we will study the different methods of preparation, physical properties, as well as chemical properties. So these are the various things we are going to study about each and every type of hydrocarbon. So today I am starting with the first variety of hydrocarbon that is alkanes. So every type of an organic compound we follow a particular pattern in our study guys. So actually first thing we discuss about them is some general introduction. okay and then we study something about the naming later if they show any isomerism special isomerisms then we discuss about them and later we will go for their preparations so how can we prepare alkanes in a different way by different reactions so all the preparation reactions the preparation methods we will discuss in a detailed way and later we will go for studying something called physical properties see under physical properties uh we discuss very very general aspects like boiling point melting point solubility you know so all those things will come under physical properties and finally the most important part is chemical properties so under chemical properties we discuss how they react with what type of compounds they react and what type of products you get out of them, right? So it's like their uses. So what do we discuss in chemical properties? It's their uses. Uses here means the way they react, what are the different special reactions they undergo, which are the new, new organic compounds that you can prepare from these guys. You know, all of them we will discuss under chemical properties. So every hydrocarbon is studied under these headings only. So first we'll discuss their introduction then naming them isomerism, preparation methods, physical properties and chemical properties. So in the entire organic chemistry chapters both in 11th and 12th every organic compound type of organic compound is studied in this pattern itself in these headings itself. So you must carefully understand the pattern like in which way we are going to study these types of compounds. Okay fine. So let us start with the first variety alkanes. So what we have to discuss the first thing is introduction. So today in this video I am going to complete the introduction part, naming part and isomerism. Okay and in my next video I am going to complete the preparations of alkanes. Then in the third video, I'm going to complete the physical properties as well as chemical properties of alkanes. Okay, so this is how about alkanes, I will complete the concept in three different videos. Fine. So let's quickly go to the topic, the general introduction about alkanes. So we all know Alkanes are nothing but you know carbon-carbon single bond having hydrocarbons. So these are the hydrocarbons which have only carbon and hydrogen and between carbon atoms you only have single bonds. So that is the first point to be remembered and now the second point is every carbon in Alkyl is sp3 hybridized okay so you must have an idea about this hybridization guys so about this hybridization we have discussed in my previous chapter right so what way you can identify that which carbon has what the hybridization all of that we have discussed so any carbon which has got single bonds around it then that carbon will always show sp3 hybridization okay so whenever you have sp3 hybridization then the bonds around such carbon is always arranged in a tetrahedral fashion isn't it so bonds the four bonds which are there around every carbon is always there in what shape it is there in a tetrahedron shape right okay so all of that we already know fine And one major thing is these alkanes are also called with the name paraffins. So what do you mean by paraffin? Paraffin in the sense little affinity. So they are the organic compounds which show little affinity. Affinity in the sense attraction. Okay, affinity is nothing but they are very very less reactive. So what do you mean by? this word, these alkanes are actually inert. I can say inert or less reactive with other substances. Okay, so they are actually inert at room temperature. So at room temperature, you know, these alkanes do not react with acids, they do not react with bases and they do not react with any substances. That is why they are called with the name paraffins so it's a greek word para is nothing but little affines affinity means what attraction so they always show very very little attraction towards other compounds okay that means uh in a normal language what we can say is they are not at all i mean they are very very less reactive they are inert at room temperature okay so if you want to see their reactions you can only observe at high temperatures so at room temperature they do not react with any chemical substance so that is the reason we call alkanes as paraffins Fine and these alkanes will have a general formula CnH2n plus 2. So what do you mean by n here? n is nothing but number of carbon atoms. So whenever you have carbon atom 1 then what will be the formula of alkane? It will be CH4 right? So substitute 1 in place so what do you get C1H2 into 1 2 plus 2 4 so the first member of alkane is CH4 what do we call its name we call this alkane as methane so we had seen all these in the nomenclature right so I'm not going into much details about the naming of alkanes because it is already covered in one of my video called nomenclature of hydrocarbons okay saturated or aliphatic branched hydrocarbons you know there is a video the link is provided in the description you can go and check it out so in this video i'm not actually covering the naming part because as a whole i have already completed right Okay, so just the few members I will list it out here. So the first member of alkane is methane which is the second member. How do you write the formula? It is C2H6, right? So how do you write its elaborate formula? CH3 bond CH3. So this is called with the name ethane. So whenever you have two carbon atoms, we have to use the word eth. Since carbons have all single bonds, we are using a suffix a n e right so we call its name as ethane so now the next member is ch3 ch2 ch3 isn't it so this is called with the name propane right so like that it continues ch3 ch2 ch2 ch3 is called with the name butane right okay so actually these are very very simple and basic alkanes where you have only the straight chain. Okay, so you may have many number of carbon atoms in a chain. And you may have complicated alkanes like a branched alkane also. So you just observe this alkane here, right? So it has heavy branches, isn't it? So this is one of the alkane with so many carbon atoms and you know, with some branches, right? So it can have a huge branches or small branches, anything, you know, about their naming, everything we have discussed in that video, right? Fine. So these are the different types of alkanes actually. I mean to say that the alkane can be as simple as this and it can be as complicated as this also. So you have different alkanes with different carbon atoms and different shine lengths. Okay. So this is some general introduction about alkanes and about the naming I'm not covering here as I said. So straight away I will go for the next important topic that is isomerism. So what actually we mean by isomers here? See isomers are nothing but we are comparing between two compounds. Say this is one alkane this is another alkane. So we are just finding out what is similar between them and what is difference between them. Okay. So studying this itself, we will call it as isomerism. So I have one alkane, the other alkane. What is similar? What is difference? Right. So this is what we mean by isomerism. So let's quickly go for isomerism and what are the different isomerisms that you can study and observe in case of alkanes. Right. See students here, there are two types of isomers possible in case of alkanes. Actually, in case of isomerism, you have different types of isomerisms. So, among so many isomerisms, you know, two important types of isomers you will observe in case of alkanes. They are chine isomers. The first variety is chine isomers and then second variety of isomerism That is isomers that you observe here is conformational isomers. Okay, so conformational isomers. So this is really very important. Okay, so let's discuss what do we mean by shine isomers. So as the name suggests here. The similar point between two alkane is molecular formula. Molecular formula will be similar but the chain lengths are different. I told you know isomers are nothing but it's a comparison between two alkanes here. Okay so what is similar here? Molecular formula is similar but chine length, the structural formula is different. Okay. So let me write its definition now. The chine isomers are nothing but the two alkanes, two alkanes having same molecular formula but different chine lengths. Okay. different chyne lengths. So such isomers are called as chyne isomers. So let's talk about the chyne isomers now. Fine. So suppose you have an alkane methane, right? So how many ways you can write this? There's only one carbon. So how many ways you can write its chyne? Say the chyne has only one carbon. There is only one way of writing the formula, right? There is only one way of writing a structure. So how do you write the structure here? Just the four hydrogens, we will show it around. So in this case, you know, chyne isomerism is not possible, right? So suppose you have two carbon containing alkane. So what is a two carbon containing alkane? CH3 is CH3. So this is the only way of writing two carbon atoms. So writing this is... Similar to writing this. So anyway, so the chyne, you know, this is the only possible way of writing a chyne. So even in this case, you will not observe chyne isomerism. Coming to the third variety of alkane that is propane, CH3, CH2, CH3, right? So how many ways can you introduce any branches here? So writing this is similar to writing this. So writing Something like this is similar as writing this. So this is a chain, this is a chain, both names are proper, right? So they cannot make isomers. What I told you, formula has to be same, chain length is different, okay? So the structural formula has to be different. So in these three cases, chain isomerism is not possible. So if you want to observe chain isomerism, you should at least have 4 carbon atoms in a chain. 4 carbons in a chain you must have. So only then chain isomerism is observed. Now let's go for four carbon atoms having alkane, okay, to observe chain isomerism, that is C4H10, okay. So, how many ways this C4H10 can be written? So, one is a straight chain compound, right. So, one is this CH3CH2CH2CH3. So, what is its formula? C4H10. What is its name? We will call it as butane. It can be called as butane, right? So what is the other way of writing a structure for this formula? I can also write C4H10 as CH3CHCH3CH3. See, one of the CH3 I have introduced as a branch in between, isn't it? So what is the formula here? How many carbon atoms? It is 4. How many hydrogen atoms? It is 10. You see, this compound has C4H10. This compound also has C4H10 formula but both are entirely different. This is called as just butane or n-butane whereas this is called with the name isobutane. So remember anything you put as a branch then we use the prefix iso in a common nomenclature okay so butane has a different property isobutane may show a different properties actually both are different compounds but what is similar between them similarity is molecular formula what is difference between them difference is the way you write the structure the chain lengths are different here you have a single linear chain but this is a branch design you Okay, so this is what we mean by chain isomerism. Remember, such chain isomerism is observed in alkanes, but it cannot be observed in one carbon, two carbon, three carbon containing alkanes. It cannot be seen. Whereas to observe this chain isomerism, our alkane must at least have four carbon atoms. Okay, so now questions will be asked like this. So how many possible chain isomers can be observed for C4H10? So how many isomers that you can observe? Two, right? So two chain isomers you can observe. What are they? One is n-butane, the other one is isobutane, right? So if I ask you a question, how many isomers are possible for the alkane which has a formula C5H10? 12 that is pentane. So pentane shows how many chain isomers. So how many ways you can write this pentane, right? How many different structures you can show this C5H12. So that's what you will have to try. So can you able to try, just pause the video and try how many ways you can write C5H12, right? So the way we have written C4H10 can be written in only two possible ways. Can you think of any possible way of writing this? No. only two possible chain isomers are formed in case of C4H10. Likewise, try writing chain isomers of C5H12. See guys, for C5H12, one way of writing is that linear one, CH3CH2CH2CH212345th carbon, that is EH3. So, this is called as N-pentane. right. So whenever carbon atoms are arranged in a single linear fashion then we use this letter N. N means normal okay it's a normal sign so N pentane it is. So the other way of writing is I can introduce any branch here see CH3 CH CH3 CH2 CH3. So if I ask you to write the IUPAC name how do you write the IUPAC name here? It is you know one two 3, 4, isn't it? So it is 2-methylbutane. 2-methylbutane is the IUPAC name. So this is another way of writing C5H10. See, even this guy has the formula C5, sorry, H12, isn't it? So second isomer. Coming to the third isomer, how can I write C5H12? Highly branched structure, something like this. CH3, So what will be the IUPAC name of this compound? 1, 2, 3, right? So this can be 2,2-dimethylpropane. isn't it so or in short it can also be called as neopentane so neopentane is a common name but 2,2-dimethylpentane is the IUPAC name okay so even this particular compound has a formula C5H12 so can you think of writing any other way for C5H12 Say if you write something like this CH3CH2CHCH3CH3. Okay, will this be an isomer? Actually, this is similar to this only. If you try naming this, you will start numbering this way, right? So, this is also 2-methyl butane only. So whenever the IUPAC names are matching, they are not isomers. Actually for the China isomers, you will have different different names. So when you had got different names, then they are isomers, China isomers. When two compounds which have got a same name in the sense, they are similar, they are not the different compounds. So isomers are actually different compounds but something is similar between them and something is different right. So this is the way of checking whether it can become isomer or not. So any two structures which had got same name in the sense they are not isomers okay. Actually this and this is similar so you cannot show this as the fourth isomer here. okay so uh you know there are only three possible one is this second one is this third one is this so c5 h12 can show how many china isomers only three okay so like that can you all try for showing isomers for c6 h14 c7 h16 c8 h18 c9 h20 and C10H22. See, it's all trial and error. You will have to, you know, use your idea of drawing structures in various possible ways. Okay. See that the formula must match. Names should be different. Right. See, for C5H12, we had observed 3 chain isomers. For C4H10, we have observed 3. two chain isomers like that for c6 h14 can you tell me how many isomers are possible right so you can pause the video and try in your book that how many ways you can write the structures for c5 for sorry for c6 h14 okay so check with the structures and tell me how many uh chain isomers can be possible for c6 h14 right fine so anyway i will give you one shortcut trick to remember okay so the number of isomers possible for these guys usually for the competitive exam they'll ask you for c7 h16 how many china isomers are possible for c6 h14 how many china isomers are possible so every time you know you can't draw and check it out right sometimes you may get confused and you will get messed up with the things so it's better to remember something okay to give the answer in a best possible way so this trick will definitely help you for any competitive exam guys so we have observed for c4h10 2 isomers for c5h12 three isomers are possible likewise for c6 h14 five chain isomers are possible for c7 h16 nine isomers are possible and here 18 here 35 and here 75 okay so these are the magic numbers that you can remember okay so uh i told you to put the structures for c6 h14 no so you will get five isomers so try putting the structures in your book right So this is all about the chain isomerism. So for the chain isomers, what is similar? Molecular formula is similar for all the three structures. But the structures, the way you write the chain, chain lengths are very much different. Okay, so hope you had got an idea about the chain isomerism. Now we will go for another important isomerism that is conformational isomers. See guys, conformational isomerism is a very different isomers. You should visualize the things very very carefully to understand this conformational isomers. See it's very simple. Here the similarity is molecular formula and structure. Structure is also similar. Okay, so the two isomers which have similar molecular formula, similar structure, you know, let me write the definition first. Isomers have same molecular formula and structure but arrangement of atoms, arrangement of atoms in space. in space is different. So why do these atoms arrangement gets changed in a space time to time? It is because the C-C bond which is there between the two carbon atoms can be rotated easily. You know that bond can be moved easily, it can be rotated. That's the reason you know the atoms which are arranged in a space. will change their position. Okay, so time to time. So those isomers are called with the name conformational isomers. So what we have to write here, the arrangement of atoms in space is different due to free rotation. This is very, very important due to free rotation of carbon-carbon single bond. Okay, you should at least have carbon, one carbon-carbon single bond. So that carbon-carbon single bond can be rotated very, very easily. It has free rotation. Okay, so that's the reason the arrangement of atoms in a space will be different. I'll show you with one ball and stick model. So let us learn the confirmations of ethane here. So confirmations or conformational isomerism. in ethane okay because ethane is a very simple alkane how do you write ethane two carbons right between them you have a single bond this carbon has three hydrogens and this carbon also has three hydrogen so i'll show ethane with the help of ball and stick model guys so to understand in a better way about conformational isomerism i have got this ball and stick model see The black color balls are there, no? They are carbon atoms. So this carbon has three hydrogens. Even this carbon also has three hydrogens. Okay, fine. So this is your ethane. So initially, you just check how these hydrogens are there in a space. They are there in a particular position, right? So now, this bond is there, no? The bond between carbon and carbon can be freely rotated. See, it can rotate. It can freely move like this. So... As I move the bond like this, the hydrogen atom's position is changed. Now, previously it was in some position. See, now they are in some position. As I rotate, you know. Now the position of hydrogens in space is different, right? So as this bond gets rotated, you know, the hydrogen atom's position gets changed in a space. So this is one isomer, this is another isomer, this is the third isomer. See, as I rotate, I get different, different isomers because the arrangement of atoms in a space is different, right? See, the structure is same, molecular formula is same, just what is difference? Arrangement of atoms that is particularly the hydrogen atoms in space is getting different. Right? So this is one isomer. I rotated. This is another isomer. Again I rotated the bond. This is the third isomer. Again I rotated. This is the fourth isomer. Again I rotated. This is the fifth isomer. Like that, hundreds of conformational isomers are possible in case of alkane. Okay, so this is ethane. Here hundreds of isomers are actually possible guys. So we don't have names for all those conformational isomers but two conformational isomers are very very important to study. We have given names for them. They are nothing but you know staggered conformer, staggered conformer and eclipsed. eclipsed conformer. Okay. So what do you mean by staggered and eclipsed conformer? That is what we are going to study. Okay. So you understood now what do you mean by conformers? So all these are say this is one conformer. Again rotated second conformer. Again rotated third conformer. So as you keep on rotating the arrangement of hydrogen atoms in a space gets different. Right. So that is what we call conformers or Confirmers are also called with the name rotamers. Okay, conformational isomers have another name. We can call them as rotamers also. Isn't it? Okay, so now you just observe one thing guys. Okay, you observe. See, I am going to talk about staggered conformer and eclipsed conformer. So, these staggered conformer is the most stable conformer actually, the most stable structure. Eclipsed conformer is least stable structure. Least stable structure. So, I can represent these structures in two different way. First one is I can represent them. I can show it on a board or we can write it on a paper in two different ways. Okay. So one is by Newman projection. One is by Newman projection formula. Okay. The other one is by Sahaar's projection formula. we can draw their structures with the help of two formulas guys one was by newman projection formula by sahar's projection formula okay so there are two different ways of writing their formulas or structures fine So what do you mean by Newman projection formula? How do we write a staggered conformer and eclipsed conformer with the help of Newman projection formula? It's very very simple. You just see, put a dot, this is like a front carbon you know. See I am holding this ethane like this, so this is your front carbon and this is your back carbon. So the front carbon, I have shown it like a dot. The front carbon has You know three hydrogens right? Later we will put and this is your back carbon okay. So this is front carbon which I indicated like a dot and the carbon which is behind which you cannot see actually it's behind that we have represented as a circle. So the front carbon has three hydrogens they are these and the back carbon also has three hydrogens right? So this is one hydrogen, this is second hydrogen and this is third hydrogen. So this is what we call staggered conformer. So staggered conformer is written like this. Okay, so if you observe staggered conformer, you know. If you observe staggered conformer, you know the bonds of front carbon and the bonds of back carbon are actually far away with each other. So you know such a conformer can be more stable guys. So if you can observe this is what the staggered we say. Okay. So these hydrogens and these hydrogens, there is a nice gap. Actually you see. this white color ball and this white color ball you see actually nice gap is there between them okay got it So enough distance is there between hydrogen atoms of front carbon and hydrogen atoms of backside carbon. So when you have this enough distance, repulsions will be minimum, right? Bonds, if two bonds are very near, bond is nothing but a pair of electrons. If two bonds are very near, you will observe lots of repulsions. But if the bonds are very far, if they are far away with each other, repulsions are minimum, no? Whenever repulsions are minimum, the compound gets more stability. So that is the reason we say staggered conformer is more stable. Okay, so this is how the staggered conformer looks guys. Okay, so nice distance is there between hydrogen atoms of front carbon and back carbon. CH bonds have got nice distance, they stay far away with each other. So now as I rotate a bond, you know, the staggered conformer will get disturbed, it becomes some other conformer. I'm again rotating. it has become some other conformer i am again rotating it has become some other conformer and now you see this if you can look at this okay hope you can see this if you can look at this actually you don't have enough uh distance between this bond and this bond right there seems to be very near so if the distance is reduced if the bonds are very near you will observe lots of repulsion, right? So more energy, less stable. So this conformer is called with the name eclipsed conformer. So how do we represent eclipsed conformer? Same. This is front carbon, this is back carbon. So these are the hydrogens of front carbon, right? So these are the hydrogens of back carbon. You see? The hydrogens of front carbon and back carbon, the distance is very little, right? Like you observe here, you observe from your angle, you see the distance between this ball and this ball is very very little, isn't it? So, if the distance is very little, I mean bond interactions are too high, the structure become less stable, okay? So, this conformer is called with the name Ecclest. Then remaining all confirmers between staggered and eclipsed, lots of rotations are possible, right? Lots of confirmers are possible, right? All of them collectively called with the name skew confirmers. Skew confirmers. So what do you mean by skew confirmers? It is the confirmers that come in between staggered and eclipsed. Staggered and eclipsed. okay say for example this is what i said this is eclipsed isn't it because you know wait because this bond and this bond is very near this is eclipsed and now you know this is actually staggered staggered and automatically at a time the structure will not be changed into staggered see this is eclipsed slowly slowly you know the bonds moving slowly slowly again this is another conformer again this is another conformer now you see Now you got staggered. So after many confirmers, you are getting staggered. And now as I rotate after many confirmers, you will get eclipsed. So between staggered and eclipsed, there are many confirmers, right? So they are all collectively called with the name skew confirmers. Okay. So among hundreds of confirmers, because many ways I can rotate the bond, many ways the bond can be freely moved. So as it moves, you get a different, different arrangements. They are called confirmers, as I said. So Among hundreds of confirmers, we are concentrating only two confirmers. One is the most stable confirmer that is called as staggered. The other one is less stable confirmer that is called as eclipsed. So this is the way of representing staggered and eclipsed by Newman projection formula. And then by using Sahaar's formula, it's different. Say this is one carbon, this is another carbon. So usually these are the hydrogens of this carbon and these are the hydrogens of this carbon. So actually this is the staggered conformer I represented with the help of Sahaar's projection formula. Okay and eclipsed how do we represent that sir this is the C-C bond this is one carbon this is another carbon you know H H, H, okay, so H, see hydrogen atoms are actually slightly near, okay, so this is what we call eclipsed, eclipsed conformer which I have shown with the help of Sahaar's projection formula, okay, so So, usually Newman projection formula is very important and it is in this conformer you can clearly visualize that you can say that yes the hydrogens of front carbon and back carbon is far away so that repulsions are minimum so stability is more and here you can clearly visualize the hydrogen atoms are very near so stability is very less repulsions are very much high. Okay fine and actually speaking. The CC free rotation, CC bond free rotation is hindered by these bond repulsions guys and that bond repulsions are called with a special name called torsional strain. Torsional strain. So what do you mean by torsional strain? This is nothing but repulsions between the bond you know repulsions. between the bonds, okay, between the bonds that disturbs, okay, so that disturbs CC bond rotation that can hinder the CC bond rotation I can say, okay. So, in case of staggered conformer, torsional rotation torsional strain is very much minimum in case of eclipsed since the bonds are very near repulsions are more so cc bond rotation is also hindered to some extent okay so we say torsional strain is very much high in eclipse torsional strain is very much low in case of staggered okay so this is actually their stability relative stability always depends on so called torsional strain Okay, so this is all about staggered conformer and eclipsed conformers of ethane guys. Okay, so this is one of the special isomerism you will observe in alkane. So why this isomerism is observed? It's all because of that CC bond is freely rotated. Okay, so that's why the arrangement of atoms in a space gets different that leads to the formation of so many conformational isomers. Okay. So that's all about today's video. We have discussed the two important types of isomers in case of alkanes. In my next video, I will come up with the preparation methods of alkanes. So how can we prepare alkanes by different methods? All of them we will discuss. Okay. So till then, revise the concept and do subscribe our channel to learn the concepts in the easiest way. Thank you so much guys. All the best.

Hey all, welcome to Homeschool. Hope everybody are doing good. And I am with Class 11 Chemistry. The chapter is Hydrocarbons.

Hydrocarbons is one of the most important chapters in case of organic chemistry. In my previous videos, I discussed every aspects of basic organic chemistry, isn't it? We discussed how to name organic compounds, different organic compounds having different functional groups, about their naming, about their classification and we had seen very very basic aspects of organic reactions. So how they react, what way they react and what are the different electronic effects that we observe in organic compound.

So everything we discussed in a detailed way and coming to this chapter. this is just the continuation of organic chemistry where you are going to study about the chemistry of the most important and basic organic compounds so here we will try to understand how a class of alkanes can be prepared and how they react okay so we know what was alkanes we studied in the previous chapter Alkanes are nothing but single bond containing organic compounds. They do not contain any functional group. You just observe carbon and hydrogen.

So after all, that is what the definition of hydrocarbons is, isn't it? So hydrocarbons are. the organic compounds which have only carbon and hydrogen you will not find any functional group isn't it so we are going to study the detailed aspects of such hydrocarbons so what are the different hydrocarbons that you can observe first variety is alkane second variety is alkenes isn't it so alkenes you will observe double bonds between carbon atoms. And the third type of hydrocarbon is alkynes.

So in case of alkynes, you will observe triple bond between carbon atoms, isn't it? And the fourth type of hydrocarbon, the most important variety that is aromatic hydrocarbon. So about these organic compounds you are going to study in a chapter.

So what do we study about them? We just study about the basic introduction. So we'll try to understand how these things can be reactive, whether they can be reactive or not, if reactive, what way they react.

you know, all of them. And then we will study about their nomenclature and then certain aspects of isomerism. Then we will study the different methods of preparation, physical properties, as well as chemical properties. So these are the various things we are going to study about each and every type of hydrocarbon. So today I am starting with the first variety of hydrocarbon that is alkanes.

So every type of an organic compound we follow a particular pattern in our study guys. So actually first thing we discuss about them is some general introduction. okay and then we study something about the naming later if they show any isomerism special isomerisms then we discuss about them and later we will go for their preparations so how can we prepare alkanes in a different way by different reactions so all the preparation reactions the preparation methods we will discuss in a detailed way and later we will go for studying something called physical properties see under physical properties uh we discuss very very general aspects like boiling point melting point solubility you know so all those things will come under physical properties and finally the most important part is chemical properties so under chemical properties we discuss how they react with what type of compounds they react and what type of products you get out of them, right? So it's like their uses. So what do we discuss in chemical properties?

It's their uses. Uses here means the way they react, what are the different special reactions they undergo, which are the new, new organic compounds that you can prepare from these guys. You know, all of them we will discuss under chemical properties.

So every hydrocarbon is studied under these headings only. So first we'll discuss their introduction then naming them isomerism, preparation methods, physical properties and chemical properties. So in the entire organic chemistry chapters both in 11th and 12th every organic compound type of organic compound is studied in this pattern itself in these headings itself.

So you must carefully understand the pattern like in which way we are going to study these types of compounds. Okay fine. So let us start with the first variety alkanes.

So what we have to discuss the first thing is introduction. So today in this video I am going to complete the introduction part, naming part and isomerism. Okay and in my next video I am going to complete the preparations of alkanes. Then in the third video, I'm going to complete the physical properties as well as chemical properties of alkanes.

Okay, so this is how about alkanes, I will complete the concept in three different videos. Fine. So let's quickly go to the topic, the general introduction about alkanes.

So we all know Alkanes are nothing but you know carbon-carbon single bond having hydrocarbons. So these are the hydrocarbons which have only carbon and hydrogen and between carbon atoms you only have single bonds. So that is the first point to be remembered and now the second point is every carbon in Alkyl is sp3 hybridized okay so you must have an idea about this hybridization guys so about this hybridization we have discussed in my previous chapter right so what way you can identify that which carbon has what the hybridization all of that we have discussed so any carbon which has got single bonds around it then that carbon will always show sp3 hybridization okay so whenever you have sp3 hybridization then the bonds around such carbon is always arranged in a tetrahedral fashion isn't it so bonds the four bonds which are there around every carbon is always there in what shape it is there in a tetrahedron shape right okay so all of that we already know fine And one major thing is these alkanes are also called with the name paraffins. So what do you mean by paraffin?

Paraffin in the sense little affinity. So they are the organic compounds which show little affinity. Affinity in the sense attraction. Okay, affinity is nothing but they are very very less reactive.

So what do you mean by? this word, these alkanes are actually inert. I can say inert or less reactive with other substances. Okay, so they are actually inert at room temperature. So at room temperature, you know, these alkanes do not react with acids, they do not react with bases and they do not react with any substances.

That is why they are called with the name paraffins so it's a greek word para is nothing but little affines affinity means what attraction so they always show very very little attraction towards other compounds okay that means uh in a normal language what we can say is they are not at all i mean they are very very less reactive they are inert at room temperature okay so if you want to see their reactions you can only observe at high temperatures so at room temperature they do not react with any chemical substance so that is the reason we call alkanes as paraffins Fine and these alkanes will have a general formula CnH2n plus 2. So what do you mean by n here? n is nothing but number of carbon atoms. So whenever you have carbon atom 1 then what will be the formula of alkane? It will be CH4 right?

So substitute 1 in place so what do you get C1H2 into 1 2 plus 2 4 so the first member of alkane is CH4 what do we call its name we call this alkane as methane so we had seen all these in the nomenclature right so I'm not going into much details about the naming of alkanes because it is already covered in one of my video called nomenclature of hydrocarbons okay saturated or aliphatic branched hydrocarbons you know there is a video the link is provided in the description you can go and check it out so in this video i'm not actually covering the naming part because as a whole i have already completed right Okay, so just the few members I will list it out here. So the first member of alkane is methane which is the second member. How do you write the formula? It is C2H6, right? So how do you write its elaborate formula?

CH3 bond CH3. So this is called with the name ethane. So whenever you have two carbon atoms, we have to use the word eth. Since carbons have all single bonds, we are using a suffix a n e right so we call its name as ethane so now the next member is ch3 ch2 ch3 isn't it so this is called with the name propane right so like that it continues ch3 ch2 ch2 ch3 is called with the name butane right okay so actually these are very very simple and basic alkanes where you have only the straight chain.

Okay, so you may have many number of carbon atoms in a chain. And you may have complicated alkanes like a branched alkane also. So you just observe this alkane here, right? So it has heavy branches, isn't it? So this is one of the alkane with so many carbon atoms and you know, with some branches, right?

So it can have a huge branches or small branches, anything, you know, about their naming, everything we have discussed in that video, right? Fine. So these are the different types of alkanes actually. I mean to say that the alkane can be as simple as this and it can be as complicated as this also. So you have different alkanes with different carbon atoms and different shine lengths.

Okay. So this is some general introduction about alkanes and about the naming I'm not covering here as I said. So straight away I will go for the next important topic that is isomerism. So what actually we mean by isomers here?

See isomers are nothing but we are comparing between two compounds. Say this is one alkane this is another alkane. So we are just finding out what is similar between them and what is difference between them.

Okay. So studying this itself, we will call it as isomerism. So I have one alkane, the other alkane. What is similar?

What is difference? Right. So this is what we mean by isomerism.

So let's quickly go for isomerism and what are the different isomerisms that you can study and observe in case of alkanes. Right. See students here, there are two types of isomers possible in case of alkanes. Actually, in case of isomerism, you have different types of isomerisms.

So, among so many isomerisms, you know, two important types of isomers you will observe in case of alkanes. They are chine isomers. The first variety is chine isomers and then second variety of isomerism That is isomers that you observe here is conformational isomers. Okay, so conformational isomers. So this is really very important.

Okay, so let's discuss what do we mean by shine isomers. So as the name suggests here. The similar point between two alkane is molecular formula. Molecular formula will be similar but the chain lengths are different.

I told you know isomers are nothing but it's a comparison between two alkanes here. Okay so what is similar here? Molecular formula is similar but chine length, the structural formula is different. Okay.

So let me write its definition now. The chine isomers are nothing but the two alkanes, two alkanes having same molecular formula but different chine lengths. Okay.

different chyne lengths. So such isomers are called as chyne isomers. So let's talk about the chyne isomers now.

Fine. So suppose you have an alkane methane, right? So how many ways you can write this? There's only one carbon.

So how many ways you can write its chyne? Say the chyne has only one carbon. There is only one way of writing the formula, right?

There is only one way of writing a structure. So how do you write the structure here? Just the four hydrogens, we will show it around. So in this case, you know, chyne isomerism is not possible, right?

So suppose you have two carbon containing alkane. So what is a two carbon containing alkane? CH3 is CH3.

So this is the only way of writing two carbon atoms. So writing this is... Similar to writing this. So anyway, so the chyne, you know, this is the only possible way of writing a chyne.

So even in this case, you will not observe chyne isomerism. Coming to the third variety of alkane that is propane, CH3, CH2, CH3, right? So how many ways can you introduce any branches here?

So writing this is similar to writing this. So writing Something like this is similar as writing this. So this is a chain, this is a chain, both names are proper, right? So they cannot make isomers. What I told you, formula has to be same, chain length is different, okay?

So the structural formula has to be different. So in these three cases, chain isomerism is not possible. So if you want to observe chain isomerism, you should at least have 4 carbon atoms in a chain.

4 carbons in a chain you must have. So only then chain isomerism is observed. Now let's go for four carbon atoms having alkane, okay, to observe chain isomerism, that is C4H10, okay.

So, how many ways this C4H10 can be written? So, one is a straight chain compound, right. So, one is this CH3CH2CH2CH3. So, what is its formula?

C4H10. What is its name? We will call it as butane.

It can be called as butane, right? So what is the other way of writing a structure for this formula? I can also write C4H10 as CH3CHCH3CH3. See, one of the CH3 I have introduced as a branch in between, isn't it? So what is the formula here?

How many carbon atoms? It is 4. How many hydrogen atoms? It is 10. You see, this compound has C4H10.

This compound also has C4H10 formula but both are entirely different. This is called as just butane or n-butane whereas this is called with the name isobutane. So remember anything you put as a branch then we use the prefix iso in a common nomenclature okay so butane has a different property isobutane may show a different properties actually both are different compounds but what is similar between them similarity is molecular formula what is difference between them difference is the way you write the structure the chain lengths are different here you have a single linear chain but this is a branch design you Okay, so this is what we mean by chain isomerism.

Remember, such chain isomerism is observed in alkanes, but it cannot be observed in one carbon, two carbon, three carbon containing alkanes. It cannot be seen. Whereas to observe this chain isomerism, our alkane must at least have four carbon atoms. Okay, so now questions will be asked like this. So how many possible chain isomers can be observed for C4H10?

So how many isomers that you can observe? Two, right? So two chain isomers you can observe.

What are they? One is n-butane, the other one is isobutane, right? So if I ask you a question, how many isomers are possible for the alkane which has a formula C5H10?

12 that is pentane. So pentane shows how many chain isomers. So how many ways you can write this pentane, right? How many different structures you can show this C5H12. So that's what you will have to try.

So can you able to try, just pause the video and try how many ways you can write C5H12, right? So the way we have written C4H10 can be written in only two possible ways. Can you think of any possible way of writing this? No. only two possible chain isomers are formed in case of C4H10.

Likewise, try writing chain isomers of C5H12. See guys, for C5H12, one way of writing is that linear one, CH3CH2CH2CH212345th carbon, that is EH3. So, this is called as N-pentane. right. So whenever carbon atoms are arranged in a single linear fashion then we use this letter N.

N means normal okay it's a normal sign so N pentane it is. So the other way of writing is I can introduce any branch here see CH3 CH CH3 CH2 CH3. So if I ask you to write the IUPAC name how do you write the IUPAC name here?

It is you know one two 3, 4, isn't it? So it is 2-methylbutane. 2-methylbutane is the IUPAC name.

So this is another way of writing C5H10. See, even this guy has the formula C5, sorry, H12, isn't it? So second isomer. Coming to the third isomer, how can I write C5H12? Highly branched structure, something like this.

CH3, So what will be the IUPAC name of this compound? 1, 2, 3, right? So this can be 2,2-dimethylpropane.

isn't it so or in short it can also be called as neopentane so neopentane is a common name but 2,2-dimethylpentane is the IUPAC name okay so even this particular compound has a formula C5H12 so can you think of writing any other way for C5H12 Say if you write something like this CH3CH2CHCH3CH3. Okay, will this be an isomer? Actually, this is similar to this only. If you try naming this, you will start numbering this way, right?

So, this is also 2-methyl butane only. So whenever the IUPAC names are matching, they are not isomers. Actually for the China isomers, you will have different different names.

So when you had got different names, then they are isomers, China isomers. When two compounds which have got a same name in the sense, they are similar, they are not the different compounds. So isomers are actually different compounds but something is similar between them and something is different right. So this is the way of checking whether it can become isomer or not.

So any two structures which had got same name in the sense they are not isomers okay. Actually this and this is similar so you cannot show this as the fourth isomer here. okay so uh you know there are only three possible one is this second one is this third one is this so c5 h12 can show how many china isomers only three okay so like that can you all try for showing isomers for c6 h14 c7 h16 c8 h18 c9 h20 and C10H22.

See, it's all trial and error. You will have to, you know, use your idea of drawing structures in various possible ways. Okay. See that the formula must match.

Names should be different. Right. See, for C5H12, we had observed 3 chain isomers. For C4H10, we have observed 3. two chain isomers like that for c6 h14 can you tell me how many isomers are possible right so you can pause the video and try in your book that how many ways you can write the structures for c5 for sorry for c6 h14 okay so check with the structures and tell me how many uh chain isomers can be possible for c6 h14 right fine so anyway i will give you one shortcut trick to remember okay so the number of isomers possible for these guys usually for the competitive exam they'll ask you for c7 h16 how many china isomers are possible for c6 h14 how many china isomers are possible so every time you know you can't draw and check it out right sometimes you may get confused and you will get messed up with the things so it's better to remember something okay to give the answer in a best possible way so this trick will definitely help you for any competitive exam guys so we have observed for c4h10 2 isomers for c5h12 three isomers are possible likewise for c6 h14 five chain isomers are possible for c7 h16 nine isomers are possible and here 18 here 35 and here 75 okay so these are the magic numbers that you can remember okay so uh i told you to put the structures for c6 h14 no so you will get five isomers so try putting the structures in your book right So this is all about the chain isomerism. So for the chain isomers, what is similar?

Molecular formula is similar for all the three structures. But the structures, the way you write the chain, chain lengths are very much different. Okay, so hope you had got an idea about the chain isomerism. Now we will go for another important isomerism that is conformational isomers. See guys, conformational isomerism is a very different isomers.

You should visualize the things very very carefully to understand this conformational isomers. See it's very simple. Here the similarity is molecular formula and structure.

Structure is also similar. Okay, so the two isomers which have similar molecular formula, similar structure, you know, let me write the definition first. Isomers have same molecular formula and structure but arrangement of atoms, arrangement of atoms in space. in space is different. So why do these atoms arrangement gets changed in a space time to time?

It is because the C-C bond which is there between the two carbon atoms can be rotated easily. You know that bond can be moved easily, it can be rotated. That's the reason you know the atoms which are arranged in a space.

will change their position. Okay, so time to time. So those isomers are called with the name conformational isomers.

So what we have to write here, the arrangement of atoms in space is different due to free rotation. This is very, very important due to free rotation of carbon-carbon single bond. Okay, you should at least have carbon, one carbon-carbon single bond. So that carbon-carbon single bond can be rotated very, very easily.

It has free rotation. Okay, so that's the reason the arrangement of atoms in a space will be different. I'll show you with one ball and stick model. So let us learn the confirmations of ethane here. So confirmations or conformational isomerism.

in ethane okay because ethane is a very simple alkane how do you write ethane two carbons right between them you have a single bond this carbon has three hydrogens and this carbon also has three hydrogen so i'll show ethane with the help of ball and stick model guys so to understand in a better way about conformational isomerism i have got this ball and stick model see The black color balls are there, no? They are carbon atoms. So this carbon has three hydrogens.

Even this carbon also has three hydrogens. Okay, fine. So this is your ethane.

So initially, you just check how these hydrogens are there in a space. They are there in a particular position, right? So now, this bond is there, no?

The bond between carbon and carbon can be freely rotated. See, it can rotate. It can freely move like this. So...

As I move the bond like this, the hydrogen atom's position is changed. Now, previously it was in some position. See, now they are in some position. As I rotate, you know.

Now the position of hydrogens in space is different, right? So as this bond gets rotated, you know, the hydrogen atom's position gets changed in a space. So this is one isomer, this is another isomer, this is the third isomer.

See, as I rotate, I get different, different isomers because the arrangement of atoms in a space is different, right? See, the structure is same, molecular formula is same, just what is difference? Arrangement of atoms that is particularly the hydrogen atoms in space is getting different. Right? So this is one isomer.

I rotated. This is another isomer. Again I rotated the bond. This is the third isomer.

Again I rotated. This is the fourth isomer. Again I rotated. This is the fifth isomer. Like that, hundreds of conformational isomers are possible in case of alkane.

Okay, so this is ethane. Here hundreds of isomers are actually possible guys. So we don't have names for all those conformational isomers but two conformational isomers are very very important to study.

We have given names for them. They are nothing but you know staggered conformer, staggered conformer and eclipsed. eclipsed conformer.

Okay. So what do you mean by staggered and eclipsed conformer? That is what we are going to study. Okay.

So you understood now what do you mean by conformers? So all these are say this is one conformer. Again rotated second conformer. Again rotated third conformer.

So as you keep on rotating the arrangement of hydrogen atoms in a space gets different. Right. So that is what we call conformers or Confirmers are also called with the name rotamers.

Okay, conformational isomers have another name. We can call them as rotamers also. Isn't it?

Okay, so now you just observe one thing guys. Okay, you observe. See, I am going to talk about staggered conformer and eclipsed conformer. So, these staggered conformer is the most stable conformer actually, the most stable structure. Eclipsed conformer is least stable structure.

Least stable structure. So, I can represent these structures in two different way. First one is I can represent them. I can show it on a board or we can write it on a paper in two different ways.

Okay. So one is by Newman projection. One is by Newman projection formula. Okay.

The other one is by Sahaar's projection formula. we can draw their structures with the help of two formulas guys one was by newman projection formula by sahar's projection formula okay so there are two different ways of writing their formulas or structures fine So what do you mean by Newman projection formula? How do we write a staggered conformer and eclipsed conformer with the help of Newman projection formula?

It's very very simple. You just see, put a dot, this is like a front carbon you know. See I am holding this ethane like this, so this is your front carbon and this is your back carbon. So the front carbon, I have shown it like a dot.

The front carbon has You know three hydrogens right? Later we will put and this is your back carbon okay. So this is front carbon which I indicated like a dot and the carbon which is behind which you cannot see actually it's behind that we have represented as a circle.

So the front carbon has three hydrogens they are these and the back carbon also has three hydrogens right? So this is one hydrogen, this is second hydrogen and this is third hydrogen. So this is what we call staggered conformer. So staggered conformer is written like this.

Okay, so if you observe staggered conformer, you know. If you observe staggered conformer, you know the bonds of front carbon and the bonds of back carbon are actually far away with each other. So you know such a conformer can be more stable guys.

So if you can observe this is what the staggered we say. Okay. So these hydrogens and these hydrogens, there is a nice gap.

Actually you see. this white color ball and this white color ball you see actually nice gap is there between them okay got it So enough distance is there between hydrogen atoms of front carbon and hydrogen atoms of backside carbon. So when you have this enough distance, repulsions will be minimum, right? Bonds, if two bonds are very near, bond is nothing but a pair of electrons. If two bonds are very near, you will observe lots of repulsions.

But if the bonds are very far, if they are far away with each other, repulsions are minimum, no? Whenever repulsions are minimum, the compound gets more stability. So that is the reason we say staggered conformer is more stable.

Okay, so this is how the staggered conformer looks guys. Okay, so nice distance is there between hydrogen atoms of front carbon and back carbon. CH bonds have got nice distance, they stay far away with each other.

So now as I rotate a bond, you know, the staggered conformer will get disturbed, it becomes some other conformer. I'm again rotating. it has become some other conformer i am again rotating it has become some other conformer and now you see this if you can look at this okay hope you can see this if you can look at this actually you don't have enough uh distance between this bond and this bond right there seems to be very near so if the distance is reduced if the bonds are very near you will observe lots of repulsion, right?

So more energy, less stable. So this conformer is called with the name eclipsed conformer. So how do we represent eclipsed conformer?

Same. This is front carbon, this is back carbon. So these are the hydrogens of front carbon, right?

So these are the hydrogens of back carbon. You see? The hydrogens of front carbon and back carbon, the distance is very little, right?

Like you observe here, you observe from your angle, you see the distance between this ball and this ball is very very little, isn't it? So, if the distance is very little, I mean bond interactions are too high, the structure become less stable, okay? So, this conformer is called with the name Ecclest. Then remaining all confirmers between staggered and eclipsed, lots of rotations are possible, right? Lots of confirmers are possible, right?

All of them collectively called with the name skew confirmers. Skew confirmers. So what do you mean by skew confirmers?

It is the confirmers that come in between staggered and eclipsed. Staggered and eclipsed. okay say for example this is what i said this is eclipsed isn't it because you know wait because this bond and this bond is very near this is eclipsed and now you know this is actually staggered staggered and automatically at a time the structure will not be changed into staggered see this is eclipsed slowly slowly you know the bonds moving slowly slowly again this is another conformer again this is another conformer now you see Now you got staggered. So after many confirmers, you are getting staggered. And now as I rotate after many confirmers, you will get eclipsed.

So between staggered and eclipsed, there are many confirmers, right? So they are all collectively called with the name skew confirmers. Okay.

So among hundreds of confirmers, because many ways I can rotate the bond, many ways the bond can be freely moved. So as it moves, you get a different, different arrangements. They are called confirmers, as I said.

So Among hundreds of confirmers, we are concentrating only two confirmers. One is the most stable confirmer that is called as staggered. The other one is less stable confirmer that is called as eclipsed. So this is the way of representing staggered and eclipsed by Newman projection formula. And then by using Sahaar's formula, it's different.

Say this is one carbon, this is another carbon. So usually these are the hydrogens of this carbon and these are the hydrogens of this carbon. So actually this is the staggered conformer I represented with the help of Sahaar's projection formula.

Okay and eclipsed how do we represent that sir this is the C-C bond this is one carbon this is another carbon you know H H, H, okay, so H, see hydrogen atoms are actually slightly near, okay, so this is what we call eclipsed, eclipsed conformer which I have shown with the help of Sahaar's projection formula, okay, so So, usually Newman projection formula is very important and it is in this conformer you can clearly visualize that you can say that yes the hydrogens of front carbon and back carbon is far away so that repulsions are minimum so stability is more and here you can clearly visualize the hydrogen atoms are very near so stability is very less repulsions are very much high. Okay fine and actually speaking. The CC free rotation, CC bond free rotation is hindered by these bond repulsions guys and that bond repulsions are called with a special name called torsional strain. Torsional strain.

So what do you mean by torsional strain? This is nothing but repulsions between the bond you know repulsions. between the bonds, okay, between the bonds that disturbs, okay, so that disturbs CC bond rotation that can hinder the CC bond rotation I can say, okay. So, in case of staggered conformer, torsional rotation torsional strain is very much minimum in case of eclipsed since the bonds are very near repulsions are more so cc bond rotation is also hindered to some extent okay so we say torsional strain is very much high in eclipse torsional strain is very much low in case of staggered okay so this is actually their stability relative stability always depends on so called torsional strain Okay, so this is all about staggered conformer and eclipsed conformers of ethane guys. Okay, so this is one of the special isomerism you will observe in alkane.

So why this isomerism is observed? It's all because of that CC bond is freely rotated. Okay, so that's why the arrangement of atoms in a space gets different that leads to the formation of so many conformational isomers. Okay. So that's all about today's video.

We have discussed the two important types of isomers in case of alkanes. In my next video, I will come up with the preparation methods of alkanes. So how can we prepare alkanes by different methods? All of them we will discuss.

Okay. So till then, revise the concept and do subscribe our channel to learn the concepts in the easiest way. Thank you so much guys. All the best.

Transcript for:Introduction to Hydrocarbons and Alkanes

Transcript for:
Introduction to Hydrocarbons and Alkanes