Draw all possible resonance structures for the reactive interm...

Question

Draw all possible resonance structures for the reactive intermediates shown.

(b) Chemical structure diagram showing a benzene ring with a carbonyl group and a reactive intermediate for resonance structure analysis.

Accepted Answer

All right. Hi everyone. So first question, let's go ahead and illustrate all valid resonance structures for the following molecule. And the molecule in question here is cyclo pen three E in one on. But specifically it is an Enola right. This is an ol stemming from our cyclo pen three in one. Oh So before we begin, let's go ahead and recall a couple of things that are true about resonance structures. Right? First of all, resonance structures are representations of the same molecule that differ only in the movement of electrons. Right. So it's important to acknowledge that the molecular formula doesn't change and the connectivity between atoms in the molecule does not change either. The only thing that does is the positioning of electrons in the molecule now to illustrate the movement of electrons to form one resonance structure compared to another, we use curved arrows, right? And we use double headed curved arrows to showcase that there are two electrons moving at one time. Mhm Additionally, right, when illustrating the movement of electrons, it's important to remember that electrons in a resonance structure, they move from an area of higher electron density right to an area of lower electron density. And the way in which you can tell whether or not an area has a higher electron density is by looking at the chart, right? And what you'll notice is that our starting material is in fact an ol which is an anion, right? And so there's going to be a region that has a negative charge and therefore has the highest electron density, which we can see here in between our car and the. So from here, in order to generate our resonance structures, we understand that the anion that's in between the carbon and the alkene is going to be what's moving here, right? Because that represents the area of highest electron density. Mhm And on either side of it, on either side of the anion itself are two regions of lower electron density because we have two regions on either side of the anion that have a neutral charge, right. So that indicates lower electron density. Now here, what you'll notice is that first of all, the car bono and the alkene both contain pi bonds that can move around, right? And there's a sigma bond, a single bond separating the anion from these pi bonds. So what that means is that both of our resonance structures are going to entail the lone pair of electrons on our carbon here moving and occupying those signal bonds in between the car boal or the all key, right? Because it has space to do so right, those sigma bond provides space for the lone pair of electrons to jump around, so to speak. So for our first structure, which I'm going to illustrate in blue here, the loan pair of electrons can go ahead and jump in between the carbon it's originally on and the car bono itself, right. So that's going to form a double bond in between carbons one and two. But we also have to acknowledge that there's another movement of electrons going on at the same time, right? Because if we keep the carbon on carbon one and we also form a double bond in between carbon one and two, that violates the octet of carbon one, right, because carbon one would have way too many electrons. So because of that the pi electrons of the carbon are going to shift upwards towards oxygen to kind of make space for this new double bond to form in between carbons one and two. So because of that, right, we can go ahead and draw our first structure. Here's our cyclo pentin ring, the double bond between carbons three and four is untouched in this particular resonance structure. But instead, here we have a new double bond in between carbons one and two and the car bono is instead an O minus. So this is one structure, right? And now on the starting material on our original molecule, I'm going to erase the blue arrows so that I can illustrate how we form the second resonance structure. So the second resonance structure involves the movement of this loan pair of electrons in between carbons two and three, right? Because for the first one, we approached the car bottle, but now this time, we can go ahead and approach the all. So that's what I'm going to do. The loan pair of electrons on carbon tube is going to go ahead and jump in between carbons two and three. And just like in the first one, right, there has to be a simultaneous movement of electrons from the pi bond, right? Because otherwise carbon three here would have way too many electrons and therefore violate the octet. So because of that, the pi electrons in between carbons three and four are going to be pushed towards carbon four, right. So instead of an O minus, we get another carb anion just in a different location. Yeah, wasn't happy with the way I drew that. So if here our cycle pentane ring and this time the car bono has remained untouched, but now we have a double bond in between carbons two and three and we have a carbon ion at position four. And so here are your two final or rather your valid resonance structures, right? You have the starting material itself and then you have the two resonance structures that form as a result of that carbon ion moving to either side of itself. All right. So with that being said, if you stuck around to the end. Thank you so much for watching and I hope you found this helpful.

Draw all possible resonance structures for the reactive intermediates shown.
(b)

Key Concepts

Resonance Structures

Reactive Intermediates

Electron Delocalization

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