Which of the following pairs represent resonance structures? (LO 7.13) (a)(b)(c)

Video transcript

welcome back everyone among the given pairs of molecules. What are resonant structures. So we're going to begin with our first pair where we would recognize that in order to get to this resonant structure here, we would have to have shifted this lone pair as a pi bond between oxygen carbon here, which would ultimately create too many bonds on this carbon atom, causing this pi bond to have to shift as a lone pair on this carbon atom, which is why As a result we would see this carbon atom have a total of two bonds to hydrogen And then its original third bond here. However, with this lone pair on itself, it now has one more valence electron directly attached to itself than it would prefer, which it would prefer to have four since it's in group four a. However, it now has five directly attached valence electrons to itself, which is why it has this minus one formal charge. Whereas this oxygen, because we shifted one of its lone pair electrons as a bond now between this oxygen atom and this carbon atom, we now have a plus one formal charge on this oxygen atom, since it only has +12345 directly attached fans electrons to itself. Where oxygen being in group six A would prefer to have six directly attached fans, electrons. So based on these facts, we can confirm that choice A is a set of resonant structures. So we would rule or we would actually confirm that it is a correct choice as resonant structures. So so far we have one correct answer being choice A. Let's move onto choice B where we end up with this second structure as a resident structure according to choice B. Now, in order to get to this second structure, we can possibly craft a resonance by shifting one of our pi bonds where we can just go with this pi bond, which would shift here and this would result in a structure where we have the following outline. We still have that pi bond in that position, but we now have a pi bond in this position where this nitrogen atom still has a lone pair on itself, which we would not want to draw there. We would actually want to draw the lone pair here on the outside where the nitrogen will then have its original bond to hydrogen. And because we shifted the pi bond from this location to this location, we're now going to have a plus one formal charge at this carbon atom as well as a minus one formal charge at the nitrogen atom here because it will have 123456 directly attached valence electrons to itself, which is one more than I would prefer being five since nitrogen is in Group five A. So because according to choice B, we have this bond to hydrogen here. We would actually disagree with this pair being a set of resonance structures. This would not occur. So we would rule this out, we would agree that this would be the correct resonant structure to replace this one. So we would say B is not resonant structures and we would roll choice be out as an incorrect choice. Moving on to choice see we have these two structures given So in order to create a resonance structure here, we can imagine shifting one of our pi bonds between oxygen and nitrogen to a location between nitrogen and oxygen here on the other half of the molecule, which will create a resonance structure where we have this left hand oxygen now singly bonded to nitrogen, where our nitrogen still has its radical electron on itself and on the right hand side, nitrogen is doubly bonded to oxygen where this oxygen still has its three sets of lone pairs and the oxygen on the left still has its two sets of lone pairs on itself and as far as formal charges because we recognize that oxygen prefers to have six directly attached valence electrons to itself. This right hand oxygen, we would count a total of 12345678 directly attached electrons, meaning it has two more than it would prefer. So it has a formal charge of minus two. Our oxygen on the left hand side has a total of 12345 directly attached electrons, meaning it has one less than it would prefer. So it would have a formal charge of plus one and then our nitrogen atom having a radical on itself has a total of +1234 directly attached electrons, so it has one less than it would prefer, which would be five. So it has a formal charge of plus one as well. And so because we know that this structure should be the resident structure, we would disagree with this structure being a resident structure, having a triple bond here. And so we would rule out choice C because this does not represent a pair of resident structures. So our only correct anti choice to complete this example is going to be pair A, which represented a correct pair of depicted resonance structures. So I hope that everything I reviewed was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video.