a. Draw resonance contributors for the following species. Do n...

Question

a. Draw resonance contributors for the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are major contributors and which are minor contributors to the resonance hybrid.
b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?
3.

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

3. Chemical structure of a benzene ring with a carbonyl group and a methyl group, illustrating resonance contributors.

Accepted Answer

All right. Hi everyone. So for this question, let's go ahead and draw the significant resonance contributors of the following structure. Do all the resident contributors contribute equally to the resident hybrid, if not identify the major and minor contributors to the resident hybrid. So first and foremost, right, recall that in resonance, we have a de localization of electrons, whether they be through high bonds are lone pairs throughout a molecule, right? And the different ways in which we can move those electrons around results in different resonance forms or resonance structures. Now when you go ahead and you combine all resonance forms of one particular compound and you take the average of them, so to speak, you get what's known as the resonance hybrid, but as you generate different resonance forms, right, the properties of each are not going to be the same. So because of that, we have to consider how those different properties affect their contribution to the residents hybrid because the more stable a resonance form is the more it contributes to the resonance hybrid compared to another less stable residence for. So let's go ahead and draw all of our contributors. And the first thing I'm going to do is I'm going to go ahead and draw the les structure of my starting material Benz aldehyde. And so I'm going to go ahead and essentially copy this molecule the way that I've, it's drawn on the screen here, except here, I'm going to make sure that I'm showcasing all of my loan pairs of electrons. And the reason I'm doing this is because this is actually one of my resonance forms. So now let's go ahead and recall a few things because here the movement of electrons during resonance takes place between either loan pairs or pie bonds but never sigma bonds, right? And additionally, when you are drawing the movement of electrons, you're going to move them towards either SP or SP two hybridized atoms, never sp three hybridized atoms. So here, right, our resonant structures are going to involve the lone pairs of electrons on oxygen, my carbon and the pi bonds of my benzene ring. So the first thing I'm going to do is I'm going to have one of the pie bons in my benzene ring move towards the carbonnel towards the sp two hybridized carbon atom. And that by contrast is going to go ahead and force the pipe bond of my car bottle to shift upwards towards oxygen. So that results in my first or my second resonance structure in which now I have a carbo ion and a double bond between a ring carbon and my carbon carbon and now my carbon oxygen has a negative charge. So now, right, because I have a conjugated pie system in my benzene ring, then my carbo cad ion is going to go ahead and circle around the benzene ring itself. So my second P one is going to go ahead and move over and that is going to once again shift the position of my positive charge and my car bottle stays untouched, right? My oxygen is still going to have a negative church. So now my carbo catt ion is still circling around, right. So now my last pie bond in the benzene ring is going to move. So now what we've done here is we've essentially circled back. Two are starting carbonnel only on the opposite side. So here, right, my last resonance structure is going to feature the restoration of the benzene ring and of my car bottle because the lone pair of electrons on oxygen is going to go ahead and regenerate the car bottle and that's going to force the pie bond between carbons here to go back to the bing ring. And that completes my resonance because notice how we've come back to our starting benz aldehyde. And so these are all of my resonance forms, but like I mentioned previously, right? And not all resonance forms may contribute equally because as soon as we generate different resonance forms, what we're doing is we're changing the molecular properties of each. So the reason why all resonance forms do not contribute evenly or equally is because we have to consider the relative stability of one over the other. So let's talk about that, right. What I want to bring to your attention is the fact that two of our resonance structures are, well, all of them are neutral, right overall, but two of them have no separation of charge, whereas three of them do have separation of charge. Now recall that when a resonance form has a separation of charge between two atoms, it is going to be less stable. So because of that right, my three resonance structures with my carbo CAD ion and my negative charge on oxygen, they're going to be minor contributors because that separation of charge makes them less stable. But my two that have no separation of charge are going to be my major contributors by contrast and there you have it, right. These are all of the resonance contributors and because their molecular properties have changed as a result of resonance, right? Not all resonance forms contribute equally because the more stable a resonance form is the more it is going to contribute. So I know that was a lot, right? But if you stuck around to the end, thank you so much for watching. And I hope you found this helpful.

Key Concepts

Resonance Structures

Major and Minor Contributors

Equal Contribution of Resonance Contributors

Watch next