 Hello friends, welcome back. Today again in this session, we are going to discuss the next you know the application of various electronic effects which is nothing but the acid and base strength. If you remember, we have already discussed the acid and base strength when we have done inductive effect. How to compare acid and base strength on the basis of inductive effect. Now, since we have covered all those important factors or electronic effects right important factor and electronic effects, then we are going to apply all those electronic effects and compare the acidic strength. So, here we have discussed all those electronic effects. So, now we are going to apply all those electronic effects and identify the acid and base strength. So, you see first we are going to difference discuss acidity or acidic strength right. You see like we have already discussed that in organic chemistry we have defined acidic nature with respect to water molecule with respect to H2O. And acid are those compounds which provides H plus ion in its aqueous solution right. So, it increases the concentration of H plus ion in the aqueous solution. Suppose we have H A and when you put this into water it forms H 3 O plus plus A minus H 3 O plus plus A minus. So, this is what this H A is an acid since it produces H plus ion and that H plus ion is taken up by this H2O molecule. And this is a base right tendency to accept H plus ion this has tendency to accept H plus ion this acid this becomes again base and this is acid right. So, here you see acid when loses H plus ion after losing H plus ion whatever is left that we call it as conjugate base right. So, A minus is the conjugate base of H A acid and when base accepts H plus ion whatever we get we call it as conjugate acid right. So, H A you see this acid H A and A minus we can call it as conjugate acid base pair conjugate acid base pair. Similarly, H 2 O and H 3 O plus also it is conjugate acid base pair right. So, H 2 O H 3 O plus is a conjugate acid base pair H A A minus is a conjugate acid base pair. If you observe this the conjugate acid and base differs by one H plus ion ok means we have one H plus ion extra here in comparison to this ok. So, all those molecules are conjugate base of each other when they have difference in one H plus ion. For example, suppose if you ask me to write down the conjugate base of C L it will be C L minus conjugate base of H 2 SO 4 it will be H SO 4 minus conjugate base of H SO 4 minus it will be SO 4 2 minus right conjugate base of C S 3 CO H it will be C S 3 CO O minus ok. Like this you can write down many other examples ok of conjugate acid and base pair fine. So, the acidic behavior of an acid acidity of an acid we are moving towards the next point acidity is directly proportional to the stability of of its conjugate base. Acidity is directly proportional to the stability of its conjugate base ok. More stable conjugate base more will be the acidity ok. So, suppose I will write down here right now to to compare the acidity of two acids what we will do we will just find out the conjugate base first which is actually an anion conjugate base is what it is an anion since it has a it has a negative charge on it conjugate base negative charge on it and conjugate base is nothing but when we lose H plus. So, H plus is going out it means the negative charge will be left ok. So, what we do we will compare the stability of anion more stable anion which is nothing but the conjugate base more stable is the more acidic the compound is ok. For example, you see here if we have to compare if we have to compare the acidic strength of H 2 S O 4 and H F these are inorganic acids ok. I am just taking this very basics here comparison compare the acidic strength of H 2 S O 4 and H F. So, H 2 S O 4 when loses H plus ion it forms 2 H plus plus S O 4 2 minus it is the conjugate base of it S F 4 O 4 2 minus is nothing but S double bond O double bond O O minus and O minus right and H F is H plus plus F minus right. So, here you see this molecule is more stable as comparison to F minus right this is the conjugate base of this acid. So, conjugate base of S 2 S O 4 is more stable than the conjugate base of H F which is nothing but F minus here because of equal resonance. So, since conjugate base is more stable so H 2 S O 4 is an stronger acid than H F. So, the point I am trying to make is what whenever the acid is given you write down the conjugate base of that acid right and compare the strength of conjugate base more strength more acidic the compound is ok. Now, when you talk about this conjugate base it is an anion right and how do we compare the stability of anion we have already discussed with various electronic effects like hyper conjugation inductive effect not hyper conjugation inductive effect aromaticity anti aromaticity aromaticity right mesomeric effect resonance and all. So, all those factor we will use here to compare the acidic stress to compare the stability of conjugate base and according to the stability we can say where the compound is more stable or less stable ok. Now, the acidic strength is what acidic a strength of any molecule suppose I am taking the first example H A plus H 2 O it gives what H 3 O plus plus a minus similarly the second acid I am taking is H A 1. So, A 1 A 2 or I will write B you will get confused with this H A H B 2 different acid I am taking this gives you again H 3 O plus plus B minus right since it is an equilibrium reaction. So, we can write down the equilibrium constant for this K A 1 and K A 2 right. Now, acidic a strength is what it is a strength or it is the amount of H plus ion a compound produces into the it is aqueous solution when with 1 mole of it is concentration means what if you take 1 mole per liter of this acid or 1 molar also you can write 1 molar of this acid you take the amount of H plus this and this produces into aqueous solution is nothing but the acidic strength of that particular acid ok. If it produces more amount of H plus the acidic strength of this is more than this one ok. So, acidic strength is nothing but the amount of H plus ion produces into the aqueous solution of it is of the aqueous solution of the compounds when 1 mole of that particular compound is taken right. So, if suppose if this if H A is the stronger as I am just taking a hypothetical condition if H A is the stronger acid stronger acid right then this reaction will have more tendency to go into forward direction ok and if H A is the stronger acid then it is equilibrium constant K A value will be more than to that of K A 2 more will be the K value of that acid ok. So, sometimes they also ask you to compare K A strength right they can also ask you compare the acidic strength they can also ask you the number the compare the P K A value ok. So, if K A value is more what is P K A value we have already done this it is minus log of K A right means when K A increases P K A decreases. So, if K A increases P K A decreases inversely proportional right. So, for this one we can write what P K A 1 is less than to P K A 2 right. So, to conclude this discussion what we can write that acidity or acidic strength is directly proportional to K A value and inversely proportional to P K A value directly proportional to K A value and inversely proportional to P K A value ok. So, how do we compare the acidic strength will first write down the conjugate base of this and then we compare the conjugate the stability of conjugate base. If conjugate base is more stable right then the acidity will be more and when we compare the conjugate base since it is an anion. So, we will apply all those factors of electronic effects that we have already discussed to compare the stability of conjugate base. Now, this is it the discussion of acidity and acidic strength we will see few examples on to this and we see how to apply all those electronic effects to compare the stability of conjugate base. Now, you see if you have to compare the acidic strength of these two compounds acidic strength of these two compounds ok. So, what we will do we will just write down the conjugate base of it. So, what is the conjugate base of this acid right when one H plus goes it has one lone pair on it and similarly here also the molecule will be this right. Now, we have to compare the stability of these two right. So, stability of this is what you see this has 4 pi electron and it is anti aromatic right. This is having 6 pi electron and it is aromatic right. So, stability order if you compare this is more stable right this is what we have it is a stability order of this conjugate base. So, order of stability of conjugate base is nothing but the order of stability of the compound from which that conjugate base has been formed ok. So, since this base is more stable this has more tendency to go into forward direction and loses H plus iron. Hence the acidic order will be right the second compound is more acidic than the first one ok. So, this is how you see we have prepared we have formed first the conjugate base and to apply and to find the stability of this conjugate base we are applying the concept of aromaticity. So, like this we can apply any other concept we can apply plus m minus m no plus i minus i anything that is the important part here we have. Now, the another example you see if I take this example these two molecules we have to compare the stability. Now, when we take H plus out from this molecule we get what this one and here we get again this. Now, this is what this is anti aromatic in nature negative charge negative charge and this is what this is non aromatic and non aromatic is more stable the stability order of conjugate base is this which is nothing but the acidity order of this compound right. Now, if you compare this two what is the conjugate base of this right the conjugate base of this and the conjugate base of this will be right. So, what kind of logic we can apply here this carbon is sp hybridized this is sp3 and this is sp2. So, negative charge on more electronegative atom is more stable. So, stability of this is maximum then this and then this. So, order of acidity will be what this is the most acidic compound we have then this one this is the third one acidity. Another example you see vacant p orbital here we have to compare the acidic strength here hydrogen hydrogen hydrogen and hydrogen. Now, again if you write down the conjugate base of this that will be negative charge and the conjugate base of this will be negative charge vacant p orbital. Now, here you see this oxygen has two lone pair on it only one is involved in resonance only one is delocalized. So, it has 8 pi electron 2 4 6 8 this has 2 4 6 6 pi electron. So, 6 pi electron this is aromatic but this is anti aromatic. So, this compound is more stable aromatic and hence the acidity order will be this one this one you see r c double bond o o h and r c h double bond c h o h. These are acidic hydrogen right that also you have to keep in mind the hydrogen which is attached with the electronegative element like nitrogen oxygen to some extent sulphur also we consider triple bond like this all those hydrogen which attached with the electronegative atom like nitrogen oxygen sulphur triple bond those are acidic hydrogen or active hydrogen. So, when you write down the conjugate base of it conjugate base that will be r c double bond o o minus and h plus for this the conjugate base will be r c h double bond c h single bond o negative charge 3 lone pair. Now, when you compare since here also we have resonance possible r s we can draw right pi sigma lone pair r s here also r s we can draw, but here what we have this is equal resonance it gives you equal r s. So, obviously the stability of r c double bond o o minus is more than to that of r c h double bond c h single bond o minus this is more stable and hence the compound a which is this b which is this the acidity order is a is more acidic than b. So, like this we can apply various electronic effects and compare the acidic strength. So, next session friends we will see some more examples on to this and then we will also compare the basic strength also. Thank you very much.