 it is a delocalization of pi electrons or lone pair. It is the delocalization of pi electrons or lone pair. Next line, it is the method of representation of method of representation of one molecule or ion into more than one structural unit in which more than one structural unit in which the position of pi electrons or lone pair is different. So resonance in a single line you can say it is delocalization of pi electrons or lone pair. For example, C H 3 C double bond O minus negative charge and minus means what we have three lone pairs on this oxygen atom. In this oxygen atom we have two lone pairs present. So the resonating structure of this ion is separated by this arrow. This arrow we use to represent the R S resonating structure. So when you drop the resonating structure of this, this lone pair forms a bond pair of electron and this pi electron shifts onto this oxygen atom and it gives what C H 3 C single bond O negative charge and double bond. Another resonating structure we can take the example of benzene. This is also a resonating structure because the two molecules are different. We have single bond between first and second carbon and double bond here. 3 4 5 and 6. This is the resonance. Now like I said all resonating structure or the different representation that we have, all these different representations are called as resonating structures or canonical structures, resonating structures, resonating structures, canonical structures or we also call it as contributors. Resonating, canonical or contributor. Resonating structure will take the reference of R S because this will use most of it. R S means resonating structure, canonical structure, resonating structure are the same thing. Contributors means also the same thing because all these R S contributes into the real structure. We know all these resonating structures are imaginary structures, they are not real structures. The real structure is the combination of all these resonating structures and that we call it as resonating, resonance hybrid or resonating hybrid. So resonating hybrid or the resonance hybrid for this structure is benzene and this pi electron is delocalized over the entire ring. This is the real structure, hybrid and radial structure, resonance hybrid or radial structure. For this the resonance hybrid is what C X 3, C O O and the pi electron delocalized from this oxygen to this oxygen delta negative and this is the hybrid or radial structure, hybrid or radial structure. All these things we have discussed already in chemical modeling. Now the next question is in which of the molecule the resonance is possible. When you draw the resonating structure first of all you should understand that whether the resonance is possible or not. For that we have certain conditions that condition must be satisfied by the molecule or ion then only resonance is possible. So what are those conditions that we should understand. Different different types of conditions we have different different types of conjugated system we have in all these conjugated system the resonance is possible. The first condition I will just tell you one by one ok do not write now I will just dictate you. The first condition is molecule must be plenar. Plenar molecule why it is required because delocalization means what it is the shifting of the electron pair right. This electron pair maybe it is a bi electron or non pair ok. So benzene type example if you take so this benzene has a p orbital here so there is a p orbital here also we have a p orbital ok and all these orbitals are parallel ok it is parallel and that is why the shifting of electron pair is possible. If it is not parallel not plenar then one p orbital like this another one like this so overlap is not possible. When p orbital faces each other then only overlap is possible and pi bond forms that is why plenar molecule is required for this ok. If I draw this structure you see this structure if you rotate this structure this way it means when these two p orbital overlaps it forms a pi bond right we will get a pi bond here when these two overlaps we will get a pi bond here and when these two overlaps we will get a pi bond here correct. So if I say these two are overlapping so why not these two orbital can overlap these two may also overlap right because both are parallel. So we can have overlapping of these two these two these two these two all overlap is possible that is why this pi electron continuously is continuously shift from one point to another and this denuclearization of electron is nothing but the first condition is plenar molecule white is required because then only the orbitals will be facing each other and then only shifting of pi electrons got it ok. So this way the electron keeps moving in a circle right yes but when it is next to one of the same molecules won't be attraction with the nucleus be strong so just stay there. No not possible attraction of nucleus is everywhere wherever the pi electron we have attraction will be same at every point because of this delocalization of electron it gains stability that is right. I did the center of two C atoms the force will be weak right that will attract this sigma electrons not pi electrons sigma electrons will attract but that is also that much attraction is not possible because both carbon atom has same electronity sorry same electronegativity that would attract the sigma electrons also but whatever attraction is there it is there for all the electrons but that won't affect the shifting of electrons into different orbitals got it ok. So first of all when you solve questions in organic chemistry you should have this idea that in the given molecule whether the resonance is possible ok. So how do we know that the resonance is possible for that we have certain conditions one I have told you that molecule must be plenar because in plenar molecule only the orbital will be parallel to each other and then shifting of electrons possible right. So condition right on condition condition and characteristics of condition and characteristics of resonance condition and characteristics of resonance and resonating structures. See one more thing I tell you I said that this resonating structure RS are contributors ok why these are contributors because this molecule also contributes into the real structure and this also contributes into the real structure right means some property this hybrid structure will have the property from this molecule and this molecule both means the hybrid molecule takes property or the property of hybrid molecule will be because of its all resonating structure ok. Now if this two both RS are equally stable right there are two possibilities one is what if only two RS is possible for example this one right. So this two can contribute equally into the real structure this is one possibility another possibility is what one contributes more than the other right. So in these two cases we have two types of contributors one is equal contributor another one is unequal contributors correct equal contributors are those RS which contributes equally into the real structure right means half properties the half properties equal contributors correct. Sir how will they not be equal contributors? I am not saying they are not. No sir but then we are saying in some cases there is no problem. I will discuss that I am we cannot finish resonance in five minutes I am just giving you an idea what are the possibility we can have. So it was like if you have equal contributors you will have half property from here and half property from land one what do you mean by half property? Half property means they contribute equally suppose if this structure has 10 properties you talk about venting point you talk about boundary you talk about bond is 10 bond length ok so it has certain number of properties we can define what is the bond length of this C1 C2 carbon? Bond order of C1 C2 carbon it is 2 right what is the bond order of this C1 C2 carbon? 1 so this wants that the bond order in real history should be 1 C1 C2 but this wants the bond history should be 2. So the actual bond is structure you see 1.5 that is what it means it will be in between the average of the two right in case of equal contributors but when the contribution is not equal suppose now assuming this is these two are unequal contributors right then which one will contribute more that depends upon the stability of the contributors correct if this one is more stable then this structure wants that the bond order of C1 C2 carbon should be 2 right and this wants what but since it is more stable so we can say the bond order of C1 C2 carbon should be closer to 2 because it is more stable it contributes more so we can say that the bond order of C1 C2 carbon will be in the range of 1.5 to 2 exact calculation of bond order is not possible in case of unequal contributors equal we can take average but unequal contributors we cannot find out the exact bond order of the bond right any bond but we can give you a range we can write a range of it that right like in this case if this one is more stable then obviously the bond order should be 1.5 to 2 we can say 1 to 1.5 will be there if this one is more stable understood so these are the application of resonance with resonance what we all think we can conclude the first application is to find out the bond order of the bond in a molecule okay and if you have the idea of bond order we can find out what bond strength we can find out bond length because you know bond order and bond strength are directly proportional bond order and bond length are inversely proportional all these idea we can have so one by one we will see that but first of all we write down the condition and characteristics of resonance the first condition is the molecule must be the molecule must be planar the molecule must be planar the position of atoms next one the position of atoms and the position of atoms and sigma electrons are fixed position of atoms and sigma electrons are fixed sigma electron does not take part in resonance it is always pi electrons are lone pairs but in i effect we have sigma electrons right sigma electron does not take part in resonance right next point to write down it is independent of distance independent of distance like i effect it depends upon distance right it is independent of distance in resonance next one in resonance pi electrons and lone pair pi electrons and lone pair are interconvertible lone pair can form pi bond and pi electrons can form can convert into lone pairs rs all rs are separated by all rs are separated by this double heredero this one double heredero right all rs are separated by double heredero this double heredero right on resonating structure rs does not explain all the properties of the molecule or ion the resonating structure does not explain all the properties of molecule or ion all resonating structures are imaginary or hypothetical structures these are not real structures all resonating structures are imaginary hypothetical structures for molecule to show resonance molecule or ion to show resonance so resonance it must be conjugated it must be conjugated the system must must be conjugated okay if conjugated system is there a system is molecule or ion it will be conjugated yes it must be conjugated and planar that's the two condition we have to show resonance now what is the conjugated system what is no it's not possible but C1 won't be stable because the charge it is unstable carbon cannot have five parts it has three parts you know one part is stable but we talk about stability right so the neutral carbon is more stable in charge whether it's negative or positive