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?
12.

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

12. Chemical structure of toluene with resonance contributors indicated, showing major and minor contributors to the resonance hybrid.

Accepted Answer

All right. Hi, everyone. So for this question, let's draw the significant resonance contributors of the following compound. Do all the residents contributors contribute equally to the residents hybrid if not identify the major and minor contributors to the residents hybrid. So recall really quickly that resonance structures are two or more structures of the same compound that differ only in the placement of electrons. So resonance refers to a movement of electrons or de localization throughout a molecule and the different ways in which electrons can move, results in different resonance forms or resonance structures and those resonance forms when you go ahead and combine them together and take the quote unquote average that gives you the resonance hybrid. But it's worth mentioning, right, that not all resonance forms contribute equally to the resonance hybrid because depending on the stability of one over another, the more stable resonance form will contribute more to the resonance hybrid. Now, in order to showcase our resonance here, the first thing I'm going to do is draw the Lewis structure of the compound that we're given on the screen here. So I'm drawing the same structure except here, I'm going to go ahead and showcase any loan pairs of electrons which I have on oxygen. So here, right, recall that resonance involves the movement of either loan pairs of electrons or pi bonds, never sigma bonds. And in addition to that, if I am moving electrons around, I'm always going to move my electrons towards either an SP or an SP two hybridized atom. I'm never moving electrons towards an SP three hybridized app. So here, let's look at oxygen, right, our oxygen in epoxy benzene has low pairs of electrons which do participate in resonance. But here, like I said previously, it's not going to move towards the SP three hybridized carbon atom to its right, it's going to move towards the SP two hybridized atom in the benzene ring. So that as a consequence, right, that forces the pipe on of the benzene ring to go ahead and move on to carbon. So that generates my first resonance form. So here, now I have a negative charge on my carbon in the benzene ring and there's a double wand in between carbon and oxygen which gives oxygen a positive charge. So because I have multiple double bonds within the benzene ring, then this loan pair of electrons is going to go ahead and sort of make a circle around the benzene ring itself, right. So now it's going to move towards the other pi bond in the pen ring and that's going to move that loan pair of electrons further away from oxygen. So now here's my negative charge and now it's going to happen one more time, right? So my loan pair of electrons moves and so does my carbon ion as a consequence. And here's my double bond on oxygen. So now what we've done is we've gone ahead and we circled all the way back to our oxygen. So here, right, our benzene ring is going to be restored because this carbon ion here is going to go ahead and make a pipe bond once again. And that forces the pi bond between carbon and oxygen to break and those pi electrons are going to move towards oxygen. So here, right, we end up with the original structure of the compound because now we're back at myth oxy benzene, excuse me. So these are all of the resonance forms, right? So now, like I said previously, not all resonance forms contribute equally to resonance because notice how here, right, de localization has resulted in different molecular properties for each resonance form. So because the molecular properties are different, they are going to contribute unevenly to the residents hybrid. So the answer to that question would be no, all the resonance forms do not contribute equally. But the question then becomes, which contribute more and which contribute less. Well here recall that there are multiple factors that we can take into consideration, right, one of which features a separation of charges because when there is a separation of charges then that resonance structure is going to be slightly less stable. And in addition, right, we want to look at where the charges are localized, right, because resonance structures that have positive charges on electron negative atoms are going to be less stable. Whereas if a negative charges on an electron negative atom that is more favorable. So here you'll notice that we have three resonance structures that have a positive charge on oxygen. Now a positive charge on an electron negative atom like oxygen is not the best, right. So these three are going to actually be the minor residents contribute contributors. And another reason for that is because these three resonance structures also have a separation of charge, one atom is positive and the other is negative. But here the first and final resonance form, they have no separation or charge whatsoever. So that actually makes them more stable. And that's why they're going to be the major contributors. And there you have it right. The main takeaway here is that during residence, a de localization of electrons results in different representations of a molecule known as resonance structures. Now, depending on the relative stability of one resonance form over another, some might contribute more to the resident hybrid than others. So with that being said, I know it was a lot, but if you stuck around, thank you so much for watching and I hope you found this helpful

Key Concepts

Resonance Structures

Major and Minor Contributors

Equally Contributing Resonance Structures

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