Draw the important resonance forms to show the delocalization of ...

Question

Draw the important resonance forms to show the delocalization of charges in the following ions. In each case, indicate the major resonance form(s).

j. [CH3CH=CHCH=CHCH2CH2]+
k. [CH2CH=CHOCH=CH2]+

Accepted Answer

Hey friends, let's solve this problem. It says draw the resonance forms for the following ions and mark the major contributors. What does it mean by major contributors? Well, when we have resonance forms, although there may be several different forms, the compound can take some of them have a form that is more stable than the others. So if you say took 100 of these atoms and looked at them while they're in resonance, it would likely exist in the major form most of the time. Okay, so before we draw the resonance forms, let's recall a few bits of information about resonance. So residents will happen when there's a charge, usually a charge positive or negative next to a pi bond. Okay, so when the pi bond is neighboring, when there's a pi bond on a neighboring atom to a charge that is likely for residents to occur. And I mentioned that a major form will be more stable. Well, what do we know about stability of atoms in say lewis structure? We always check for having a complete octet and having ideally no formal charges. Right, so the less of a formal charge the more stable. So we want to make sure our our major form, we can look for a complete octet. Okay, so let's dive in structure a instead of redrawing it, let's just look up here first. So we have to see if it can even participate in residence, we have our pi bond and we have a positive charge out here on the end carbon. Can this participate in resonance though? No, because it is not on the neighboring carbon. Right. If the positive charge was on this carbon that's neighboring the carbon that's involved in the pi bond. So, they would be able to be some resonance there. But the positive charges all the way out here. So, those electrons are not going to travel towards that carbon. Okay, so there are actually no resonance forms for the structure. Okay, let's look at structure B All right, let's draw it out. Carbon of the positive charge and two methyl groups next to another carbon double bonded to another carbon, oxygen. Carbon double bonnet To another carbon with two metal groups. Okay, so, I drew this out because I see a positive charge next to a carbon that's involved in a pi bond or it has a pi bond. So, the electrons from that pi bonds are going to want to move towards that positive carbon. Right, negative. Always traveling towards the positive. So, what will this look like? It looks something like this. Where did my arrows go? Did they just disappear? Did you guys see that? Oh no, I drew it up here. Not down here. I'm seeing things. So now we'll have our double bond here. I'm gonna draw it down here, single bond to carbon and then the rest of the structure is not changing. Okay, so, now, where are our charges? Well this carbons octet is satisfied, 2468 and has four electrons touching it. So, there's no charge. But now and this carbon is satisfied. But the carbon that was involved in the double bond now is not. So, it will have the positive charge over here. Okay, are there any other resonance forms that we could have here? Well, if we went back this way from this pi bond to the charge, that's the same thing as the first structure. But how about the other side of the structure? Well, that positive charges right next to lone pair. So, similarly to that double bond, there are extra electrons that can be donated towards that adam. So, we will have another resonance form that looks like this. So, the electrons from this oxygen can contribute towards that carbon double bonded carbon double bonded to the oxygen. Now the oxygen only has one lone pair. And where are our charges? Well, this carbon is satisfied now, 2468 and has 1234 electrons touching it. The oxygen donated its lone pair towards that carbon. So now it only has 12345 electrons touching it. So now the oxygen is going to have A formal charge of plus one any more resonant structures. I'm sorry, I forgot the double bond over here. Okay, well, we could have the double bond here. Go over towards the oxygen. Right, but that would violate oxygen's octet. Right? If we formed a double bond here, that would be 2468, 10 electrons. So, although we see that catching our eye with the double bond, the positive charge, we can notice that that would not occur because it would violate the octet. So, these are our resonance forms. Now we have to mark the major contributors. And remember we said that the major form of the most stable. So let's see if there's any atoms that are having an incomplete octet or a complete octet. So we could definitely check the atoms that have a charge. Right? Because all the other atoms with no charge are going to be satisfied with having octet. But if the atoms have a formal charge, sometimes they could have a complete octet and sometimes they will not. Okay, so let's check those. So let's check the carbon here. It has 246 electrons. So that's an incomplete octet. Okay, let's look at the second one. This carbon with the positive charge also has 246 electrons. So that will be an incomplete octet as well. And our oxygen here, let's see has 2468 electrons. Okay, so although they all have positive formal charges, this form is going to be our major form. This going to this is going to be our major contributor or our major resonance form because the oxygen has its complete octet. Okay, that's it for this video. I hope it was helpful. And thanks for watching

Draw the important resonance forms to show the delocalization of charges in the following ions. In each case, indicate the major resonance form(s). j. [CH3CH=CHCH=CHCH2CH2]+ k. [CH2CH=CHOCH=CH2]+

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