resonant Theory so what is resonant Theory remember we apply resonant theory for cases in which uh so there are molecules and and this is the example on on on the lecture but I'll give you another one here for example in a molecule like this and versus let's say and molecule this all right so in a molecule like this one we have basically two isolated BS remember one of the things that we learn in resonance is there are some molecules for which a single Lis structure does not give you the accurate representation of the real structure of that atom of that molecular it okay that we need to understand so in those cases we need to use a different tool in this case resonant Theory which basically what we're going to do is instead of using just one right we're going to use several resonance structure which basically several L structures and we're going to basically put these structures in Brackets and relay them by means of this Buble head Arrow right so we can have here structure a just to give you an example and then we'll have um structure B and then the we using the brackets because we want to tell people that we are actually working with resonant theories right so structure a and we can say let's say this another structure here structure B and then the structure C so when we indicating so this is the first thing that you need to understand is that when we are indicating here is that the real structure of this molecule of iron is a hybrid of structures a b and c neither of this none of these structures a b or c they do not exist remember when you have an equilibrium dollar arrow in general chemistry there is AAL between structure a and structure B because they both coexist in solution in resonant Theory we are using the brackets we using the door head arrows to show people that this A B and C are simply three different L structure that they don't exist the real molecule so the real molecule I'm going to write it over here is a hybrid of a b okay that's the number one thing that we need to understand when we have cases in which a single is not enough it's not good enough we need to go to Ral Theory and we need to then use this symbolism to show people exactly what is the structure of this molecular item now the next question is how do you know when do you have uh to apply resonant Theory to give the regular representation of a molecular ion okay so when to use resonance that's a big question and the answer to that question is whenever you find Whenever there is three or more orbital next to one another and prob line okay and and and basically what this means is um what this means basically is to have three or more SP2 three or more P because we can say here S2 I next know I'm probably so whenever you see a with three or more SP2 atoms next to one another and properly aligned you can tell that that is delocalized and because it's delocalized a single Lo structure will not be enough to show the real structure of this molecule therefore we need to use in most cases res Theory to explain the real structure of the molecule so I gave you two examples here so if we assign hydridization the struction on the right s P2 hydes carbon SP2 hydes carbon the next one is sp3 okay on this side of the molecule we have two Bond here on the right side of bond sp3 on the left side s sp3 so is this structure the localized system no because there is no there's a maximum of two and these two are atoms with the same electrity remember I gave you some material to read whenever you have uh let's say the carbon functional group right if you have a double bond in which you have atoms with different electro negativity in this case to show the B poity using the res Theory you can inde something like okay um so let me finish dra the here so two WR Pairs and then in in a case like this we have a do B withs with different you can actually say okay so there is a certain degree of delocalization it's not delocalization so basically this one is polarized right so you can show the the of the car function group and to show the resonance structures remember we use the curve power symbolism that's another thing that is very important to know in this chapter so the curve power is going to show you the flow of Pi electrons in resonance structures remember the sigma bonds they all remain the same both structur so if I were to draw the the resulting resonance structure of the curve that I drew on the left side here okay if I were to show that I going say the electrons are going toward the oxygen therefore I need to add there in the resulting molecule an extra long pair and a negative charge and then in that case because of that then the carbon is let now with three bonds therefore the carbon must be positively charged so a couple of things about this that I want to to use this example to explain how resonance Works once again in resonance structure we only show the flow of Pi electrons okay that's the only thing we show we don't move atoms we don't move Sigma bonds whatsoever that's the flow of P electron so if this and so the second thing is how to use curve arrows this is in the lecture to is in the material I gave you to read so curve are only only departing from electron sources okay electron sources that you know basically p and long pairs and they're ending the arrow is ending wherever these electons are going so they will be ending either in atom to form now a long pair as in this case or could be ending in a new Bond in a new P Bond next to the one that it was broken okay so the second thing is once you flow the electron the P electron B toward the oxygen obviously the carbon is left with positive charge the total charge of every single resonance structure is the same okay total charge here is zero total charge here is zero does this structure exist no does this structure exist no the real combination is a hybrid of both of them this is important because when you see in textbooks the carbon functional group everybody is going to draw a carbonal like this okay so you'll see this is aceton but everybody understand every organic chemist understand that even though this is what you show on the paper that is slightly contribution of structure to this real structure of this so This hybrid of these two is basically indicating that this bond is polarized that there is an of electr over the oxygen and an electron deficiency over the carbon it's exactly we have been discuss before according to electr negativity okay so you need to basically be very familiar with identifying systems in which you have uh delocalization and and and to continue with giving you another example um so we said before um that electons will be delocalized the Char or charge will be localized whenever you have two or more SP next to one another we know an SP2 atom might be an atom with a double bond another example of SP2 atoms are atoms that are for example um let me give you here an example so we have Okay so let's see so what's the name of this function of group that I have on the board Mi so that's an MI functional group uh so the first thing we need to do is to complete the L structure so if I were to complete the loose structure for this compound I will need to add basically a long pair on the nitrogen and two Ls on the oxygen right so if we want to understand if this system is a delocalized system or not we first need to assign hybridization to every single atom every atom not only carbon carbon nitrogen oxygen hens any atom right so hybridization here is SP2 obviously there is a double bond hybridization here is SP2 because of the same reason what is hybridization of the nitrogen atom from the Mi group so the the nitrogen in the Mi group is SP2 hybridized the reason for that is is because the nitrogen has a long pair and you have an with long pairs next to a double bond or next to a charge the positive charge right this atom will be SP2 hybridized so we have one SP2 two2 three SP2 atoms therefore this is indeed a localized system and we need to use resonance to show the contribution of electrons so basically remember one another thing that I want to point you're doing the the the curve H right so it's important to understand how the electrons flow in this case the long period is forming a double bond here in the next atom and then if you put a double bond right here you need to break a bond in the carbon because you don't want a carbon with five bonds obviously right so I'm going to draw the next person structure which is pretty simple and then here indicating by the arrow that this bone now is broken so we have an oxygen there so we need to add there basically a long and the charge and then obviously if the long period is on the N is going to form a door Bond now we need to place a dou b and if the B is there obviously that nitr will be positively charged so remember foral charges are very important when you're doing resal structures so the total charge of every resonance structure must be the same total charge of the structure on the left is zero to of the structure of the right is also zero okay so this is an example once again if you have ARs with double bonds they will be SP2 hybridize second example would be an atom with L pairs next to a double bond B will be also SP2 hyd and the last example that I can give you let's say let's look at this iron here okay and then my question will be if this a the localized system to answer this question we need to assign hybridization first of all we need to completely Lo structures so to complete the Lu structure I need add two L pairs on the oxygen so I'm going to do this right now one two Ls that's my new structure next I need to assign hybridization to every carbon so what is the hybridization of this carbon here sp3 no multiple bonds they so four single Bonds on that carbon so that's sp3 hybridized right then next carbon SP2 hybridized it has a b so that's Prett simple to assignation to the next to it is also P2 once again and another double bond and then what is the name of this ion by the way a carbon with a positive charge how do we call that it's a carbo so the carbon with a is a carbo okay so carbon with a charge is a carbo don't forget that and what is the hybridization of the carbon that actually Bears the positive charge what is a the hybridation is an SP2 hybridized carbon remember a carbon like that that is in the picture that I get the reading that I gave you right a carbo is a car is a carbon that isal planer the the B angle is 120 right and it does have an empty P oral so this is a structure of a carbo I okay carbo is a carbon with three single Sigma bonds one two three sigma bonds and mtyp orbital perpendicular to the plane of the molecule so it's SP2 hybridize the angle in between the sign is 120 so trional plan is a geometry the caroc is flat and there is a p perpendicular to the plane of the of the molecule in that space okay so hybridization here is SP2 and then what isation of the oxygen atom in this molecule what do you guys think so it's an SP2 hybridized because we have an with long pairs next to a charge a carbo so once again long pairs next to a double bond that's SP2 L pairs next to a carb that is SP2 as well okay so according to this picture we have one two three and four SP2 hyd bom so is this a thecal system it is so a single structure doesn't really uh show the structure the real structure of this so we need to to use resonance Theory to show the different structures right so I'm going to spend show a curve Arrow departing from the b b curve FS are always departing from electron sources in this case a p Bond and ending ending in a uh a pie bomb now a new P bom that is going to be formed so basically the P bom is moving from the left to the right so I'm going to fix that this is indicated and if if that is the case now the the positive charge is going to be over here because this carbon is going to be be left with Bond so the positive charge is going to be over here so that resonance structure is there another reson structure I need to draw for this molecule for this iron yes because we can see how so this resonance structure accounts for the delocalization toward this side of the molecule but next so to the right side I do have an also an S2 AR so I need to show that okay so once again the curve aror is departing from electron sources and is ending in this case on a new P bond that is going to be formed okay the total charge of every profal structure is the same so if if this is happening I need to then delete a long pair because obviously that long perod is being used for a new by Bond okay and if that happens now I am left with an oxygen with three bonds and that oxygen must be then positively charged okay and these will be my resonance structures so the hybrid so the real structure is a hybrid of these three structures it this is so important guys for you to see so basically that if the way I do the molecule initially and I'm going to repeat this idea the one of the most important things about resonance if you look at this molecule of this ion just like that you only see the positive charge on this carbon okay but this is a delocalized system which basically means that the positive charge the electron deficiency is shared in between between this carbon and this carbon over here because the system is delocalized because this structure does not exist the real structure is a hybrid of this three and in this hybrid the positive charge is shared between this carbon here and this carbon over here and also obviously over the oxygen okay so that's a really important thing to keep in mind the positive charge is not fully localized over single carbon because it's a delocalized system the positive charge is delocalized is Shar in between this carbon here this carbon here and the oxygen that's the real structure hybrid of this three structures we will learn in organic chemistry in the next semester that not all the resonance structures will have the same contribution to the hybrid some will contribute more than others but this is something that I want to to stop I don't want you guys to to be an expert right now just want you to know the basics about resonance okay so this is pretty much it what you need to know about resonance once again read the reading material that I gave you understand what is the res theory and practice problems problems that I gave you for inorganic and anorganic molecules okay how to use the curve AR symbolism to create resonance structures and understanding that the real thing is a hybrid of the three of them so you need to be able to molecule and assign hybridization to every single carbon atom or oxygen or nitrogen any single atom in that molecular once you assign hybridization correctly then you can determine whether or not you need to use resal structure in this example and if you do then you need to use the curve Arrow symbolism to show the structure of the uh of the