Free Chemistry NEET Video Lectures for Amines

00:>00:05 [Music] Hello everybody. I am Professor JK Ray of IIT Karakpur. Today I'd like to discuss with you some interesting topic that is organic compounds containing nitrogen or you can call it in other way nitrogen containing organic compounds. Now organic chemistry is a specialized science. By definition, it is the chemistry of carbon compounds. So I should say carbon is a must. Carbon is a must in organic compounds. One of my favorite question to the first year students was can you name an organic compound having no carbon in it?

00:01:17 You'll be surprised to know some 30 to 40% students answer inorganic benjene borazine that sort of thing but that is totally wrong because by definition the organic compounds should contain carbon so as today's topic is nitrogen containing organic compounds. So carbon is a mass. I have shown tetraalent carbon and I have attached it with a nitrogen atom. And we know carbon is tetravalent. Nitrogen is trivalent. So if you now satisfy the valencies with some substituents like hydrogen the simplest

00:02:01 one. The compound end up is methyl amine. This is the simplest carbon nitrogen containing compound methile amine or methylam amine. Now what is the nature of this compound? I mean is it alkaline or basic? Is it acidic or neutral? How one can tell? Because we know a definition for acid base as per Louis is a Louis acid is electron pair acceptor and a Louis base is electron pair donor. As the nitrogen in this case is trialent having a non-bonded electron pair. So this non-bonded electron pair it can

00:02:54 donate. So it is basic in nature or let me write down it is a base. And then question comes if I substitute some other hydrogen atom with the methyl group then what will happen? Say keeping the two hydrogen intact I put one methyl group instead of hydrogen and then the hydrogen atom over here. So this is some sort of molecular weight increase substitution increase by which in some way the electron density of the nitrogen atom will also increase. So if I compare the basic character this will be more basic than the previous one.

00:03:51 Another way if I now substitute the hydrogen of attached to nitrogen atom by the methyl group then what will be the structures? If I write that thing that one of the hydrogen being replaced by a methyl group and the other one remaining intact then what will be the nature of this compound? Answer is basic. How much is it more than the methileamine or less? If we just analyze it little bit the way I have done for the previous example that methyl group is an electron donating group because three hydrogen

00:04:34 atom attached to carbon will push electrons towards carbon. As a result the methyl group will push the electron to the nitrogen atom. So what will happen? this nitrogen electron density will increase and as per Louis acidbased theory the capability to donate electron will be more than the previous one. That means compared to methylamine inmethile amine will be more basic. And if I now increase one more methile group into the system that means in dimethile amine. Let me show the electron pair on the right hand side.

00:05:23 What will be the nature of this compound? Obviously it will be the most basic of the three or strongest among these three. Why? The reason being two methyl group will increase the electron density of the nitrogen atom. So the electron density will increase. So capability to donate electrons also will increase. So it will be stronger base. Then question come very interesting question that is it only the inductive effect which is playing is it some other effect which is also helping in the increase of basicity.

00:06:08 Answer is yes we can think about some other interesting features. What is that? Because as per Bronstead and loud concept of acid and base an acid is a proton donor a base is a proton acceptor. So what will happen if this base accepts the proton and then how the situation will take place. So let us take this example versus the methyl substituted one. What we'll see when this base picks up a proton so it will be now NH2+ and next to that this carbon having the hydrogen atom and also a methyl group.

00:07:22 What it will do? It will increase the electron density by inductive effect. At the same time, what it will do that with respect to this nitrogen which is now positively charged, there is a carbon that carbon having a hydrogen atom directly attached to that. We call this type of carbon is alpha carbon. So this hydrogen will be called the alpha hydrogen. And if there be an alpha hydrogen then this hydrogen could be shifted or the electron pair forming the carbon hydrogen bond could be shifted to the

00:08:01 carbon nitrogen system. So what we can write? We can write another interesting structure where this hydrogen is there and at the same time the proton loss will take place. The there is no bond between carbon and hydrogen atom. So what will happen? This type of situation is very interesting when there is an alpha hydrogen atom. What is an alpha hydrogen atom? With respect to a substitution from which we are taking that thing, there is a substituent next to that is the alpha carbon and any hydrogen being

00:08:51 attached to that as the alpha substituent. So that can help in a phenomena called hyper conjugation. So hyper conjugation also help to stabilize a species or an ion. And this hyper conjugation is a very interesting phenomena and that helps because we can write more no bonded resonating structure. I have written a term no bond. The hydrogen is there. H+ is being held over there. But there is no bond between carbon and hydrogen and and partially the bond has shifted. And this type of thing we should write with a

00:09:35 double-headed arrow that is symbolized for resonance or electron deoization. So electron deoization is also called resonance. And when one of these structure where we see no bond apparent bond is there then we call it as a no bonded resonance and that also help to increase the basicity of the amines. So this is also a very interesting phenomena which is found in carbon nitrogen compound with the substituents. Now let me take a very simple thing. So we do understand that a simplest compound like

00:10:27 methileamine is a nitrogen containing organic compounds. It has methyl group and an amine group. If we substitute the hydrogen atoms of the amin group by the methyl group, the electron density increases by hyper conjugation and also by inductive effect because electro negativity difference is there between carbon and nitrogen. So the bond being formed between nitrogen and carbon will be shifted more towards the nitrogen atom and that when being relayed to the next atom that is called induction and

00:11:05 that phenomena is called inductive effect and that is highly specified for the electron donating group or electron withdrawing group. We can easily identify by analyzing each bond whether a group is electron donating or a group or atom is electron withdrawing. So based on that we can write the structure and we can also calculate the electron density and see that whether a species can donate electron or can accept electron. So this electron donating phenomena when increases the basicity increases as simple as that. Now I will

00:11:46 write another very interesting thing how to know or how to prepare this type of compound very simple compound carbon nitrogen bond. One simplest way to write that thing is an arrow like this. If somewhere we write an arrow like this, this arrow is reserved for retro means reverse synthesis. So retroynthesis means reverse synthesis. I say that if we know how to make a compound, we should know how to break the compound. So now we'll take it in the carbon nitrogen bond formation. If I know how to make a carbon nitrogen

00:12:30 bond, that is the thing I'm going to talk about. I should also know how to break that thing and what are the starting materials will be needed to make this compound. So this type of arrow when being written that means it is the retroynthesis. So if I break this carbon nitrogen bond I end up with two species. One is a methyl another is NH2. But question is this methyl and NH2 is the some concept. This is not the actual species or this is not the actual molecule. So what are the starting material

00:13:12 to start with to prepare the compound like methile amine? That means how carbon nitrogen bonds could be connected with the help of what sort of starting material what are the condition. Now this concept of breaking this methileamine to methyl and amine is sometimes called these species as synths. Synthones are the concept not the actual molecule. The why I am telling these synthons are concept because this from these synthones by putting something we can get the synthetic equivalent and those synthetic equivalents are the actual

00:13:54 molecule or the starting material and if we can combine those two starting materials and in under appropriate condition then we'll get back the target molecule. So I should write methylamine in this case is TM. TM is the abbreviation of target molecule and these synths are methile and amine because this methyl may be positively charged may be negatively charged maybe a radical likewise NH2 also the nitrogen atom may be negatively charged maybe positively charged or it might be also a radical. So if I get a methile radical

00:14:36 then amine radical these are the concept these are the synthone if they recombine then we get the methylamine. Likewise if I get methile plus that is carboation amin minus they can combine plus and minus easily. So we get methylamine. If we get methile minus then I should have to get that amin plus and then also it can combine to make methylamine. And there are many other possibilities like carbon not necessarily will have to be carbonion, carboation or radical. It might be carbine. Carbine is a bivalent

00:15:13 carbon that you know having a non-bonded electron pair. And this non-bonded electrons pair may be spin opposed or spin parallel. So these type of carbines are very interesting and sometimes this carbon when being reacted with electronrich nitrogen when the electron density of that nitrogen is more we call it electrich nitrogen then what will happen they will form again the nitrogen carbon bond. So this nitrogen carbon bond formation could be done in many ways. Carboat, nitrogen anion, carbonion, nitrogen cation or carbon

00:15:58 radical, nitrogen radical or taking carbine with electronrich nitrogen or vice versa nitrine. Nitrine is is also an very interesting reactive intermediate with electrone carbon. That means all the possibilities are there but the most common or both simplest procedure is by taking methile plus. Why I'm taking methile plus? This is the concept I told you that this is the synthone. So what should be the synthetic equivalent? The synthetic equivalent will be putting the negative charge on or connecting it with an

00:16:44 electronegative element. Let us take a very good that is iodine as the electronegative element. So it will be methyl iodide. Now it is a stable molecule. I should write this is the starting material one. SM1 SN stands for starting material. Likewise, I have to take the NH2 minus because CH3 plus should combine with NH2 minus to make CH3 NH2 methylamine. So how to get NH2 minus? Again this is the synthone. I should combine it with an electropositive element. That element may be sodium, maybe potassium, maybe

00:17:27 other metals. So as simple as sodomide when treated with methyodide in NH2 in methyodide. So what will happen? The methyl iodide will react with NH2 minus. The counter ion is Na plus. So this will attack to this carbon and the carbonodine bond will break. So we will get some sort of transition state. Remember I use a term transition state where iodine is leaving and NH2 is entering the system. So this type of transition state and not intermediate. TS stands for transition state will give a product where NH2 is

00:18:23 entering from one side and iodine is leaving from the other side. So this is called an substitution nucleophilic biomolecular or SN2 type reaction. So what is SN2? S stands for substitution. N should be subscript but in capital and two should be of the same size as S not SN square. Some people say like SN². No, it is SN2. The full form is substitution nucleophilic biomolecular because in this case the two molecules are sodomide and methyliodide and this is a substitution reaction. Iodine is going out iodide and NH2 is

00:19:13 entering. So it is iodide substituted by NH2 and through a transition state and no intermediate. So it is a biomolecular reaction. So substitution nucleophilic biolecular. So in this way we are able to make the carbon nitrogen very simple compound and taking other substituents we can make ethyl nropil isopropyl tbutile nbutile isobutile all these type of amine compounds. So I can write a general formula that RNH2 is the general formula of the alkalam amine. Now these alkalamines have very interesting features because it contains

00:20:00 carbon nitrogen bond and this with this carbon there may be several substitutions or there may be unsubstituted very simple compound like methile amine. So to prepare this compound is very easy, very simple chemistry. Even methanol and ammonia could also produce. But basic concept is a simple substitution nucleophilic reaction. I told you that it is not restricted to only this type of reaction. There are several other possibilities. It may be CH3 minus reacting with N plus. But this is the one of the

00:20:41 simplest way to make the alkal amine. Now I'm just doing one more thing over here. I'm substituting one of the hydrogen of this alkalamine with a caroxilic acid group. With a caroxilic acid group C O H rest of the thing remaining intact. So RC H NH that means this was there one of the hydrogen being replaced by CO. We know CO is the abbreviation of a caroxilic group. Caroxil that is carbonil is CO hydroxil is O together it is caroxile. Now this type of compound why did I write starting from carbon nitrogen just

00:21:36 one substitution of the hydrogen by a caroxilic acid group because you know this type of compounds are present in many biologically active compound. One of the simplest compound is amino acid. What is amino acid? Amine group is present and it is also an acidic group is also present. So amino acids is a very simple compound where the NH2 and CO group both are present in the molecule. So this is also very interesting class of carbon nitrogen organic compound or I can say the nitrogen containing organic

00:22:17 compounds are very important in everyday life. One of this example is amino acids. What I have written because this is the normal trick when the caroxilic acid group is a functional group being present next carbon is called alpha next to next carbon beta next to next gamma. In that way we can go up to omega. So based on that the amino group is substituted whether in the alpha position, beta position, gamma position or delta position. We call that thing as alpha amino acid, beta amino acid, gamma amino acid, delta amino acid

00:23:00 like omega amino acid. So these amino acids are very important class of compound and this will be called alpha amino acid. And looking at this structure you can easily guess that this compound is nothing but a simply substituted. I put R is H. Then this compound is CH2 NH2 C H. And you know this compound is nothing but acidic acids. One hydrogen being replaced by an NH2 group. And this is called the alpha amino acidic acid or trivial name is glycine. Glycine is a very important amino acid. Likewise, the higher substituted or beta

00:23:52 substituted amino acid, gamma substituted amino acid could also be obtained. And those are the building block of another biologically important compound that is proteins and peptides. and peptides again being linked to polyeptides that is polymeric things of the peptide. So in that way one class of compound biologically active compounds peptides to polyeptides all those things are coming and the the review or the umbrella of carbon nitrogen compounds that is nitrogen containing organic compounds.

00:24:33 Now if I write down some of the interesting features of this compound like if I take say carbon nitrogen I told you at the beginning that carbon nitrogen bond is a must and in this case another functionality is being fixed that is CO and remaining thing let's put in this case is hydrogen And of course I have to satisfy the valency of nitrogen. So it is CH2 NH2. This is CO alpha amino caroxilic acid. So I have rewritten the glycine structure. You look at this nature of this compound. You have a nitrogen atom whose

00:25:25 valency being satisfied as 2 + 2 4 with the two hydrogen six. But this it has a non-bonded electron pair. So what this amine can do it can donate electron that we have seen. So it is a base. At the same time the same molecule in the other portion we having a caroxilic acid group CO H. We know acidic acid is acidic in nature. Caroxilic acids are acidic in nature. Why? Because if it loses proton the remaining part that is CO minus that is conjugate base gets stabilized by resonance and one of the interesting

00:26:09 feature of that resonance is we get a symmetrical resonating structure. This is the caroxilate ion which can resonate and can give the resonating structure like this. So the resonance hybrid should be written in a way that the negative charge is getting deoized over the whole region. We cannot identify which oxygen is keeping the negative charge for how many time it is getting deoized. So more the identical structure that is very important term identical structure more the stability we know calculate

00:26:58 structures contributions towards resonance hybrid is maximum. So that sort of phenomena is taking place over here. Also the caroxilate ion is getting stabilized by symmetrical resonating structures. Because of that caroxilate ion will be more stable. So the conjugate base is getting more stable. So loss of proton will be easier. So anything any species which can donate proton easily will be called an acid. So caroxilic acids are stronger acid compared to say phenol or other substituted compound. So that is

00:27:37 the reason. So you have an acidic group, you have an basic group in this molecule. So what will happen in the same molecule? One basic group is there another acidic group is there. We know a very general rule. Acid plus base give rise to salt and water. In organic chemistry we write it in this way. A very simple compound R CH2O that is a primary alcohol being treated with R prime just to make it different I have written this structure and if we treat with a caroxilic acid with a different type of alkal group

00:28:17 methile ethile etc in presence of acid mostly which not only is a good acid but also a dehydrating agent That means it takes up water. I'm giving you very simple example. Little bit of concentrated sulfuric acid is good enough. We end up with a compound that is R1 CO O C 2 R. What is this? Now this compound is nothing but a carbonial group is there and O CH2R is also there. So this type of compound is called an esther. Esther having sweet smelling mostly. So this esester functionality is very important feature for an alcohol

00:29:07 and a caroxilic acid. So alcohol and caroxilic acid when getting mixed together in presence of sulfuric acid little bit which acts as a not only acidic reagent but also a dehydrating reagent. So that helps in the production of an esther together with some water will be formed and that water will be taken care of by the sulfuric acid. So this reaction will be called eststerification reaction. So we understand that when an acidic group is present and a basic group or neutral group is present they can form an esester like

00:29:54 this. But in this case the point what we have taken that amine and caroxilic acid group what they can do because one basic group and another acidic group. One interesting feature of this is acid is a proton donor base is a proton acceptor. So what it will form it will form a species like this. What I have written? I have written that CH2 CO minus and with this CH2 the substituent is NH3+. What is this? How this is coming from the simple compound that is glycine. Answer is as the NH2 group and CO group

00:30:48 are in close proximity. One is the basic proton donor, another is an proton acceptor. So what happens in this case the base picks up the proton from the caroxilic acid group making it a caroxilate and as as I told you that caroxilate gets resonance stabilized in this way and NH3+ is also in that way is quite good. So this type of features is called joer ion or double ion one positive another negative in the same molecule. So one of the interesting features of this amino acids mainly glycine and other

00:31:26 derivatives are the joyer ion formation. Joer ion means two types of ions being formed in the same molecule where the proton transfer is taking place from the caroxilic acid group to the amine. amin is accepting it and caroxilic acid is donating it because by definition Bronstead and Lowi that a caroxilic acid group is a proton donor and a basic group is a proton acceptor. So this sort of phenomena is very much present in amino acids. I'm not going into details of other amino acid because those are the

00:32:03 building blocks of life in one sense the proteins amino acids and peptides and polymerization of that to give polyeptides all these are very much in the domain of carbon nitrogen containing compounds or I should say nitrogen containing organic compounds. So this is one class of compound but it is not only that. Now if I write going back to the amine thing that I have a caroxilic acid group and also I have an amin group and if I do a similar sort of reaction let us take by hitting that and with the help of

00:32:49 some dehydrating agent the water being taken out from that. The difference of this and the previous one is that this was in esester formation we had an alcohol and a caroxilic acid. In this case we have a caroxilic acid group and the amine group in the close proximity and being heated that means water being eliminated. So what will happen? This might happen a very interesting phenomena. It can produce a compound like this where you get a three member carbon, nitrogen and the third one is the carbonial group compounds like this. And

00:33:32 these class of compounds are very very important because I should say this type of compounds. Can you name this type of compounds? Answer is yeah. is a cyclic compound having nitrogen atom in it and also there have to be carbon in the compound. So carbon nitrogen containing three-membered ring. This is the simplest way to describe this. But this is not the only thing by which we are making the caroxilic acid and amine to combine to make a compound like this. There are many other ways but right now

00:34:12 our attention is focused on the amine and caroxilic acid intramolecular reaction. I should say in this way just to simplify this fact that O and one of the hydrogen of the NH2 is leaving as water and the remaining thing is getting cyclicized to make a hetereroyclic compound. What did I say? This is the heteroscyclic compound. Why heteroscyclic compound? Because this is the cyclic compound. No doubt to make a ring you need at least three atoms. Here carbon is one, another carbonil is second and nitrogen is third. So three

00:34:57 atoms are there. So it is a three member cyclic compound and one hetereroatom is there in the ring. So it is the heterero cyclic compound. So definition of heteroscyclic compound is now the hetereroatom containing cyclic compound. Earlier definition was it will have to be aromatic. Now it is called the aromatic heterocyclic compounds which are heteroatom containing cyclic compounds but they are aromatic in nature also. So any hetroatom containing cyclic compound should be called as heteroscyclic compound. So from simple

00:35:39 carbon nitrogen compound or amino acid we are able to get a three-membered hetereroatom containing cyclic compound and these type of compounds having another trivial name that is called lactum. Ether is one type thing and it is a cyclic. Let me put a simple example. CH2O H CO H that is alpha hydroxyaroxilic acid. If I take alpha hydroxy caroxilic acid instead of taking alpha aminoaroxilic acid and do the similar thing instead of taking the amino group I have taken the O group that is the difference CH2O CO

00:36:30 and earlier one was an example of CH2 NH2 CO this is the difference what will happen it can also form a similar sort of compound like This but this is the difference here is in the three-member ring the oxygen is there as one member in this case in the three- member ring not oxygen but nitrogen is there so these type of compounds are called lactum and oxygen containing compounds will be called lacone l what type of lacone the caroxilic acid connected to the alpha carbon which is having the hydroxy group. So this type

00:37:17 of linkage will be called alpha lacone. Okay. So three member oxygen containing heterocrayyclic compound having one next member is a carbonial group is called the alpha lacone and three member nitrogen containing heteroscyclic compound. Next to nitrogen there is a carbonial group and other carbon may be substituted or unsubstituted will be called alpha lactum. So this is the very interesting cyclic compound being obtained from the amino acid. If I take a step forward and write down another thing like CH2

00:38:00 CH2 NH2 and I put a caroxilic acid to the beta carbon amine from the amino functionality. This is the first carbon is alpha second one is beta. So this compound will be called beta amino caroxilic acid. So if I take a beta amino caroxilic acid and do a similar sort of thing what will be the product? The product will be CH2 CH2 N CO by the loss of water and there should be one more substituent and this class of compound is very very interesting. This is called beta lactum. Why betalactum? Because beta amino

00:38:54 caroxilic acids internal salt is betalactum. This is a four membered nitrogen containing heteroscyclic compound. And why did I write this thing? The answer is very simple. This type of structure or structural mui is present in many interesting compound. One of them is penicelline and you know penicelline is an antibiotic. So antibiotic activity is because of the opening up of the lactum ring where the enzyme comes and open up the carbon nitrogen bond and then this betalacttoase is the enzyme which helps. So starting from simple

00:39:50 carbon nitrogen compound we are going to the antibiotics that means I should say the betalacttoase monactum all these interesting features are coming from simple carbon nitrogen compound and uh one of the important field of carbon nitrogen compounds or importance of carbon nitrogen compound is in the antibiotic. You can name many compounds as antibiotics like penicelline everybody knows sephalosporine those are nothing but betalactum containing there are some other structural features but betalactum is very unique moi and

00:40:31 which must be present in those type of antibiotics because it kill the bacteria by certain mechanism. So three-membered four member nitrogen containing heteroscyclic compounds could be prepared very simple way and their use in everyday life is tremendous not only amino acid peptide protein but also the antibiotics and uh if I take the amin group being attached to the alipetic carbon I end up with the series of compound If I take the same amin group and attach it to the benjene ring that is also very

00:41:16 interesting feature. Say a benjin ring having an amin group. I did not say anything about the carbon nitrogen bond being attached where the carbon is an sp2 hybridized and part of an aromatic system. And looking at this you can easily write down that this type of amine we know this is nothing but anoline analine is simple C6 H5 NH2 and this compound interesting feature is it is aromatic in nature that is it has a deoized benzending we can write it in better way not only showing the localized bond but putting it a

00:42:09 deoized fashion like this. And these two are the calculate structure that is structure number one and structure number two. And we know the contribution of the resulting structure towards resonance hybrid is very important feature. If I calculate let us take this is carbon number one this is two this is three this is four this is five this is six same thing I'm writing over here and if I calculate the bond order bond order is being calculated by simple technique that what is the nature of bond between one and two let us take one

00:42:56 and two bond order I want to calculate in structure Structure number one one and two is a double bond and double bond is taken as two. In structure number two one two bond is single bond and single bond is taken as one. So if I add them together it comes three and divide by the number of resonating structure. That means how many resonating structure we are able to write one and two because this is the deoized form. This is not the calculate structure. This is overall theme being written. So this type of

00:43:38 resonating structure and their contribution to the resonance hybrid is an important feature not only to know the nature of the compound but also to find the bond order which helps us to do many things. I'll explain that. So when the added sum that is three and how many resonating structures are there that is two. So divide the sum by the number of resonating structure that is 3 by 2 that is the rule. So it comes 1.5. So what is the journal bond order of a benzene ringering where there is no substitution?

00:44:22 Answer is 1.5. How? Because take any position not only 1 2 you can go calculate for 2 3 3 4 5 6 or 61 you'll find alternate double and single bonds. So in a particular bond like as I have shown for one two for double bond it is two for single bond it is one add them sum is three divide by the total number of resonating structure in this case two it is 1.5. So bond order is 1.5. So one important feature in benjene is all the bonds are equivalent not one larger another smaller. This is in that way

00:45:03 uniform or equivalent. So 1.5 is the bond order. But if we look more precisely the what is the nature of this de localized structure we'll find there are each carbon atom having the pj orbital because all these are sp2 hybridized carbon and this pj orbital gets with the help of the electron deoized not only in the top but also in the bottom But just to clarify the thing I can say that you get a hexagonal thing and top of that or in the bottom of that an electron clouds are there. So this is overall picture of the

00:45:52 benzene ring. Why did I write that thing? Because if you break the analine molecule the way I did for alkalamine you'll end up with very difficult problem. What is that? Benjen ring as the plus, NH2 as the minus. That is very very difficult. Why? Because benzene ring having the electron cloud on top and bottom which are negatively charged. So when you bring an NH2 minus to this what will happen? They will repel. So there will be no carbon nitrogen bond formation possible. So in that way what is happening we'll

00:46:35 have to look for some other phen phenomena that means carbon nitrogen bond formation by taking benering as the plus muy or electrone deficient one and taking the amine as the electron rich will not do in other way I can say the nucleophilic substitution or the attack by the nucleophile to the simple Benjendering does not happen. Why? Because electron same electrical charge repel each other. So electron cloud are negatively charged and when you are bringing a nucleophile that is also negatively charged they will repel. So

00:47:20 what's the solution to that? Solution is very simple that if we take instead of NH2 minus NH2 plus then the problem will be solved. That means a positively charged things could make very easily attracted to the negatively charged species and I will write how this thing happens. But question come NH2 minus to NH2 plus that is reversal of polarity will be very very difficult. I'll come to that. But if I write a benjin ring in this way, a d deoized system and I bring an electrofile not minus but no plus

00:48:13 then there will be very interesting feature. So these are the substrates benzending deoized NO2 plus that is the electrofile not nucleophile. So this electrofile will come very close vicinity of the benzene ring and they will form a charge transfer complex type thing. I can write this thing in this way. There is no full bond being formed but the electrofile is taking the electron pair which is a deoized form from the benzene ring to form a complex rather to call it complex and this type of complex is

00:48:57 called a pi complex. So a pi complex is being formed by the benzene ring as a donor and nitro group as the acceptor or NO2 plus as the electrofile and benzene ring as the nucleophile because it is electronrich species. Ultimately what will happen? It will form a direct bond with the nitro group and there will be one of the benzene ring has shifted over there and there will be a positive charge on the other end. There is a hydrogen over here. There is another hydrogen in this side. So there will be a direct NO2 with the

00:49:54 benzene ring being connected. So we have got some species where the aromaticity of the benzene is temporarily lost. At the same time a new sigma bond is being formed between the carbon and the inotto group or carbon and the nitrogen. And this type of again it is a complex it is not the stable in that way. It is not a neutral molecule. So this type of complex is called sigma complex because a sigma bond is being formed. Then what happens? The hydrogen atom is being donated to make the aromaticity regain.

00:50:40 So benzene ring is now gaining its aromaticity and the nitro group is being directly attached. So what we see over here from this figure that if I treat benjene with NO2 plus I will get a pi complex where benzeneing is the donor NO2 plus is the acceptor then I will get a sigma complex where the direct carbon nitrogen bond is being formed. There is a carboation in the next carbon and then by the loss of the proton the aromaticity is regained and the substrate is being converted to the product. Product is the nitroen. So this

00:51:28 type of reaction is called electrofphilic substitution reaction. So electrofphilic substitution reaction is very common in aromatic system. So I started with alipetic systems substitution reaction that was nucleophilic substitution reaction. There directly we went from a benjene I mean the alkalamine preparation and in this case we are going from a benjene to the amin by stepwise process. Why? Because amin as such introduction is very difficult. So what we are doing we are putting a nitro group and then after

00:52:28 this nitro group is introduced then we can see that the substitution reaction has taken place. And if I ask you how can you convert this nitroen to analine? Look at this very simple answer is by reduction. By reduction means by taking hydrogen especially nent hydrogen is very good by tin or zinc and hydrochloric acid will be good enough to liberate nent hydrogen which will convert nitro to the amino group. So to sum up the things what I have discussed now that nitrogen containing organic compounds

00:53:27 are important in everyday life starting from simple amine basic compound to amino acids building block of proteins, peptides, polyeptides to another class of very interesting ing compound that is amino acids derived things like lactums alpha lactum betalactum I did not go to the gamma lactum or delta lactum also we'll explain this thing later and betalactum is the structural features present in penicelline sephalosporine and many other antibiotics so these are the very important features of the nitrogen containing

00:54:13 carbon compounds or organic compounds better to call carbogenic nitrogen compounds. And second thing is alipetic amines could be prepared very easily from nucleophilic substitution reaction. But at the same time aromatic amines to prepare you'll have to go stepwise. That means put some group which could be converted to the amine very easily. One simple example I gave you is the amine group or NH2 group and uh that could be done from nitro by simple reduction zinc hotin and hydrochloric acid.

00:54:56 So I'll continue with some other features of the aromatic nitro compounds and aromatic amino compounds so that carbon nitrogen bond will be very interesting to get some more interesting molecule. Thank you.