Which compound has the greater electron density on its oxygen ...

Question

Which compound has the greater electron density on its oxygen atom?

Chemical structures comparing electron density on oxygen in two compounds, with a question about which has greater density.

Accepted Answer

Hello everyone. Let's do this problem. It says which of the following compounds has the greatest tendency for carbon oxygen to donate an electron pair. So let's think about what will make a carbonell oxygen have a greater tendency to donate an electron pair. Well, a carbon oxygen with the most available electron or sorry lone pair electrons will increase the tendency to donate. That seems pretty self explanatory, right? So if the lone pair is more available, they're more likely to donate. So what does that mean more available? Well, what about electron density? Do you think an oxygen with higher electron density or lower electron density will be more likely to donate electrons? Definitely a higher electron density? Right. If it has more electron density more to give. So what makes an oxygen in this case, a carbondale oxygen have a higher electron density? Well, it can be increased with resonance from other atoms. It can also be decreased with resonance in the sense that the lone pair of electrons on that oxygen can be donated elsewhere around the compound. But it can also be increased in the same way where other atoms can donate their electrons towards that oxygen giving it a higher electron density. So we should look at the resonance forms of these compounds and see in which compounds the electron density is flowing towards that. Carbondale oxygen makes sense. Let's give it a shot. So in compound A, We have a six member ring, a Carbondale group coming off and then a ch three group. So in a Seattle group on a six member ring, is there any resonance here? Nope, we have the lone pair of electrons on oxygen in our double bond. But that's it. So there is no resonance, nothing will increase the electron density of that carbon oxygen. So there's no change in electron density. Okay. Well, if the other compounds have a decreasing electron density from residents, maybe that could be our answer. So let's see. Compound B we have again a six member ring and we have and Esther so and oxygen single bonded to a carbon that's double bonded to the oxygen. And then ch three group. So do we have residents here? Yep. The lone pair on this oxygen next to the ring can contribute to that partial positive carbon in the carbon L group which will break that double bond and that sends the electrons closer to that carbon oxygen, right? So that's the type of resonance I was talking about where those electrons are wanting to flow towards that carbon oxygen. So that will give six electrons or three lone pairs and a negative charge on that carbondale oxygen, a positive charge on the other oxygen. So in this case, the resonance is increasing the electron density on that carbon oxygen. Okay. So that's going to be more electron dense than a. So we can eliminate answer choice. A Alright, let's keep looking. So compound C We have a five member ring, all single bonds. And then coming off of that ring, we have a nitrogen bonded to our carbon eel group and then an ethyl group on the other side of our carbon eel. So our nitrogen has a lone pair, our carbon and oxygen has two lone pairs. So similar to structure be that lone pair on the nitrogen is next to the Carbondale group. So we will also have some residents here that nitrogen lone pair will swing down towards the partial positive carbon. Those electrons swing up onto the oxygen giving us again a higher electron density on this oxygen in our nitrogen gets a positive charge. So resonance increasing electron density on the carbon L oxygen. Okay. So we'll have to dive deeper into the differences between these two. They're the in the lead for our answer choice. But let's lastly look at compound D and see if we can rule that one out. So for compound D, we have a benzene ring that is conjugated. And then coming off of that, we have an ester group. So an oxygen bonded to the carbon L group and then a methyl group on the other side. So our single bonded oxygen gets two lone pairs are carbon and oxygen has two lone pairs. I'm going to move this into the middle because we have a couple of different ways the electrons can move here. So one way is that the lone pair on the oxygen can go towards the benzene ring, right? And then those electrons will move all around the rain. So that's increasing the electron density in the benzene ring and decreasing the electron density around the carbon eel group, right? But we also have the other possibility where the lone pair can go towards the carbonell group and have the same sort of structure as in part B actually let me move this back over. So I'll just draw out scenario, the green scenario. The second one that I just drew where those electrons move towards the carbonell group. So this structure where the electrons went to the carbon carbon is going to increase the electron density of that oxygen. But because we also have the resonance of the fennel group that's going to detract the electron density away from that carbon oxygen. So resonance with fennel detracts electron density from carbonell oxygen. So that's what I was saying, how residents can increase electron density but it can also decrease. So that's going to eliminate answer choice D so let's go back to B and C, right. These are both just increasing the electron density on that carbon oxygen. So let's look at the electrons that are donating that lone pair. So we have an oxygen atom and answer choice be highlighted in yellow. And in answer choice C we have a nitrogen. Well, let's think about the electro negativity of these two atoms because that will depend on how likely they are to donate those electrons. So oxygen is more electro negative than nitrogen. So that means oxygen is going to want to hold on to those electrons a little bit more, right? Electro negative atoms are comfortable holding those electrons, they want to hold onto them. So this oxygen and answer choice B is going to be less likely to share those electrons with the carbon oxygen, right? It's going to be selfish and want to keep those near itself. So that means nitrogen being les electro negative is happier to give away it's electrons towards that carbon oxygen. So for that reason, see compound C is going to be the one with the most available lone pair electrons on that carbon and oxygen that will have the greatest tendency to donate an electron pair. So C is the correct answer for this problem. That's it for this one. I hope this video is helpful and thanks for watching.

Which compound has the greater electron density on its oxygen atom?

Key Concepts

Electronegativity

Resonance Structures

Inductive Effect

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