 So, as we have discussed resonating structure contributors, so here we are going to discuss the relative stability of resonating structure and how do we define the relative stability of RS. So, for that we have certain set of rules and that we are going to discuss, the rule one is the structure having structure having more pi bonds is more stable. The first thing is we will just calculate the number of pi bonds, the structure which has more number of pi bonds is more stable, why is it so, because the formation of bond is always an exothermic process, formation of bond is exothermic image and hence more number of bonds, more energy releases and more will be the stability. So, you see some examples I write on here, this is A and this is B, if you calculate the number of pi bonds, number of pi bonds is more in A and the stability of A is more than to that of B, number of pi bonds in A is 2, but that of in B is 1, so stability of A is more than to that of B. This is A and this is B, here the number of pi bonds is more, so stability of A is less than to that of B. So, like this we just calculate, just we count the number of pi bonds and then according to that we will check the stability. So, the next rule is what happens if in some of the molecule we have equal number of pi bonds, then what happens for that we have rule 2, if the structure has equal pi bonds, stability decreases with chart separation, pi bonds then stability decreases with chart separation. Now, you see some examples on this, initially this is A, this is B, so number of pi bonds here is 3, here is also 3, but here we have more chart separation, so stability will be less, so A is more stable than B. Similarly, equal pi bonds more chart separation, A will be more stable than B, equal pi bonds more chart separation, A is more stable than B. Like this we can find out the priority or the order of stability of this resonating structure. So, these are the two rules we have discussed, the third rule is what happens if the molecule has equal pi bonds and equal chart separation, rule 3, if the molecule has equal pi bonds and equal pi bonds and chart separation. So, in this case what happens, the molecule having iron, molecule having more atom complete octave is more stable, the molecule and iron having more number of atoms, atoms with complete octave is more stable. For example, you see and this is B, so stability of A is more than, stability of B, the stability of A is less than to that of B, because B all the atoms having complete octave, go on as 6 electron here, here it has 8 electrons complete octave. And it is 2, B is 2, you can do this with the help of number of pi bonds also, this one is more stable because it has 1 pi bonds. So, if it is A, this is B, obviously B is more stable than A, this pi bonds also you can do or the help of octet rule also, go on as something like that. Here you see this carbon would not have the complete octet here, but here it has the complete octet, so stability of this B is more than to that of A. These are the 3 rules we have discussed according to the number of pi bonds, according to the chart separation and then the number of atoms having complete octet, okay. Now, what is rule 4? If rule 1, 2 and 3, if rule 1, 2 and 3 are fails, if 1, 2 and 3, rule 1, 2 and 3 fails, then what we can say that the negative charge more electro negative atom is more stable, positive charge on less electro negative atom is more stable, okay. Few examples I will write down here. Now, you can pause the video and solve this question I am explaining it now. First question you see, we have equal pi bonds and same charge separation, 1 pi, 1 pi, negative charge, negative charge, okay. And octet is also coming for all the atoms if you see, okay. So, you see we use rule 4 here which says negative charge on more electro negative atom is more stable. So, oxygen is carbon will have negative charge, oxygen is more electro negative. So, B is more stable than oxygen having negative charge. So, B is more stable than A, right. Here we have negative charge on nitrogen and carbon, this is A, B and C I am assuming, okay. So, first of all the two electro negative atom, the most the top two electro negative atom here we have oxygen first, then nitrogen and then carbon, right. So, which one is more electro negative oxygen, right. So, the negative charge on oxygen and nitrogen is more stable, B is the maximum. Then negative charge on nitrogen and carbon we have oxygen is more stable, then we have C and then it is, here you see negative charge on oxygen is more stable, B, A, B is more stable. There is we can find out the stability order of resonating structure. Rule 5 is positive charge is more stable when it is surrounded by more alkyne group and that is the cause of plus i, okay. And negative charge is more stable, more stable when it is surrounded by lesser number. So, here you see this carbocation is tertiary and this is primary. So, this one is more stable, this carbocation is secondary primary, secondary is more stable, this carbocation is secondary, this carbocation is tertiary, right. So, which one is more stable, secondary is more stable, okay. So, like this we can compare the stability again. Now, rule 7, rule 6, sorry, rule 6 is Fry's rule. What is Fry's rule? Molecule containing more number of benzenoid form is more stable. Benzenoid form is more stable. For example, now these two structures you compare, number of benzenoid form means what if you see this ring, it is a benzene ring, right. And this pi point we can count into this ring also, this is also a benzene ring, right. So, we have two benzenoid form here. Here you see we have only one benzene ring, this is not a benzene ring, right, because the pi point is here. So, it has only one benzenoid form. More number of benzenoid form, more stable, this is more stable than this. This compound we got as naphthalene. Number of benzenoid form here it is two, these two. Number of benzenoid form here it is only one. So, obviously two is more stable than the first one, sorry, this one is more stable than this. Now, rule 7, which is aromaticity, aromaticity, right. When the compound is aromatic it is the most stable compound, ok. The aromaticity provides extra stability to the compound, ok. What we can write aromatic compounds most stable. We will discuss this aromaticity in this resonance session only, ok. In the coming classes we will discuss this aromaticity. But one thing just you remember now, aromatic compounds are cyclic planner conjugated system. Conjugated system with n plus 2 for n plus 2 pi electrons where n is any natural number 0, 1, 2, 3 and so on, ok. Cyclic planner conjugated system with 4n plus 2 pi electrons, ok. For example, you see this molecule, right, draw the molecule here, ok. Or we can also draw this. This is b and this is c. One more thing I will tell you here. There are two more compounds we have. The stability of aromaticity is maximum then we have non-aromatic compound and in the last we have anti-aromatic compounds, ok. So, stability order is this. Non-aromatic compounds if it is non-planet or we have other condition also we will discuss all these things in detail in aromaticity when we discuss this separately, ok. Order is this. Anti-aromatic compounds all conditions are same but it only has 4n pi electron. The only difference is it has 4n pi electrons, ok. It is cyclic planner conjugated system with 4n pi electrons, ok. That is anti-aromaticity. Now if you see this compound here how many pi electrons it has? One lone pair, two, four. It has 4n pi electrons, right. So, for n is equals to 1 it satisfies this rule, right. This rule we call it as Huckel's rule for aromaticity. Huckel's rule for aromaticity. So, compound b is aromatic. Compound c has 4, 2 plus 2, 4 pi electrons, right. So, it is anti-aromatic and this compound is non-aromatic, ok. So, order of stability will be what? First aromatic, then non-aromatic and then anti-aromatic. It should be b most stable, then a and then c least stable, ok. So, with this resonance also there are chances of getting aromaticity. The compounds may become aromatic compounds, ok. According to the structure of the compound you have and the number of pi electrons it has. So, with aromaticity also the stability changes. Aromatic compounds actually are highly stable it provides extra stability to the compounds, ok. Non-aromatic compounds are the normal compounds like at the room temperature, right. Anti-aromatic is highly unstable, right. So, these are the 7 rules we have discussed to assign stability of resonating structure. On the basis of this you can easily say that which one is major contributors and which one is minor contributors. Major contributors are those molecules and ions which has more stability, right. So, if you compare these two, right if you compare this molecule the actual hybrid molecule of this, right will have the maximum property of the most stable compound which is nothing but the aromaticity, ok this b. So, this molecule will provide maximum property to the hybrid structure of this resonating structure, ok. In this two if you compare both gives you a hybrid structure, a resonance hybrid in which these two will provide property like we contributes into the property of the resonating structure. But since the second one is more stable it is major contributors this one is minor contributors, ok. So, this is what the discussion of contributing like the contributors we have is relative stability of contributors or resonating structure.