Draw resonance contributors for each of the following species and...

Question

Draw resonance contributors for each of the following species and rank them in order of decreasing contribution to the resonance hybrid. Then draw the resonance hybrid. e.

Accepted Answer

Hey everyone, let's do this problem and says, draw all the resonance contributors of the given species and predict their relative stability ease. Also draw its resonance hybrid. So let's review what is resonance. First of all, resonance structures are two or more structures of the same compound. So two or more structures of same compound and they're going to have the same connectivity, oops so equal connectivity but not the same electron distribution. Okay. So a few things to remember a few rules for resonance forms, drawing resonance forms first just start out by drawing the Lewis structure and that will be your first resonance form which they already give us here then which electrons are we going to move? Well, we only move lone pairs of electrons or pi electrons. So electrons in a double bond or a triple bond, we never move Sigma electrons or just single bond electrons and we never move atoms then where do we move the electrons to? Well, we move them towards sp and sp two atoms Never Sp three Atoms. And lastly, we're only moving around electrons, right, not adding or subtracting electrons. So the total number of electrons and the net charge on the whole structure is going to remain the same. All right. The problem also. So that's how we draw the resonance structures, right. The problem also mentioned to predict their relative stability ease. So what are some things we could look at on the structure to predict the stability? Well, we could look at the octet of the atoms. Are they complete? Are they incomplete? If it's incomplete, that's going to be less stable. Right, we can look at the charges in the compound and look at the electro negativity of the atom that is holding those charges. So if an electro negative atom has a positive charge that's going to be less stable, right? Because we know electro negative atoms love holding those electrons and vice versa. Right? If a less electro negative atom has a negative charge that will also be less stable. Also if the charges are separated over a compound that will also be less stable. So let's first draw the resonance forms and then we'll look at their stability and we'll also draw the resonance hybrid which is sort of one combination of all the resonance forms. So drawing the resonance forms, I want to move a lone pair of electrons which I see on the nitrogen and there's a neighboring pi bond. So I can make a pi bond between the nitrogen and the carbon breaking the other pi bond moving those electrons towards the positive oxygen, right? We always want the negative moving towards the positive. One of the most important concepts in organic chemistry, our methyl group is staying the same. We have a double bond to our nitrogen now and a single bond to our alcohol group, which means it has two lone pairs. Now, it had one to start with, they just didn't draw it. And again, we know that based on our valence electrons, the formal charge, right, if the oxygen had 123 electrons touching it, that means it needs two more to get five and it likes to have six. So that's where we get the plus one formal charge. So now there's no formal charge on the oxygen, but we have a formal charge on the nitrogen, 1234 electrons touching it nitrogen likes to have five. So can we move any other electrons around? No, right. The only other thing would be to move these lone pairs back down, which would be the same structure that we were given. So there are only these two resonance forms here. Let's draw the hybrid while we're already drawing and then we'll look at stability. So for drawing the hybrid first, just draw the structure, but don't draw any double bonds, okay, draw everything single bonded and don't draw the charges yet either. So now draw a dotted line where any double bonds were in any of the resonant structures. So we had a double bond between the oxygen and the carbon and we had a double bond between the nitrogen and the carbon. And now wherever there was a charge in a resonance structure, add that charge, but a partial charge unless it was on the same atom in every single structure. So for example, if the nitrogen had a positive charge in every structure, you would give the nitrogen a positive charge. But our charge was moving, the positive charge was on the oxygen first, then the nitrogen. So we give our oxygen and nitrogen partial positive charges. So that's telling us, hey, these electrons might not be here, they might be here. So there's a partial positive charge. So that is our resonance hybrid. So now we just have to predict the relative stability ease of our two resonance structures. So do all the atoms have their octet complete? Yes. What about the charges in the electro negativity of the atoms that have those charges? Well, in the first structure, we have the positive charge on oxygen. Second structure, positive charge on nitrogen. So which atom is less electro negative? Right? That one will be happier with the positive charge. Well, our nitrogen is less electro negative than oxygen. So this structure with a positive charge on nitrogen will be more stable and consequently, our structure with the positive oxygen will be less stable. So that makes be the correct answer for this problem. That's it for this one. I hope this video is helpful and thanks for watching.

Draw resonance contributors for each of the following species and rank them in order of decreasing contribution to the resonance hybrid. Then draw the resonance hybrid. e.

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