For each set of isomers, choose the isomer that you expect to be ...

Question

For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be least stable. a.

Accepted Answer

everyone. Let's look at this problem, in which we wish to predict which one of the given eyes. Mercy is most stable in which one is least stable. After careful announced because all of the four structures have multiple triple bonds. We are primarily interested in the effect of conjugation. Congregation essentially means that the double bonded carbons are linked to each other. So we have adjacent double bonds. And the greater the conjugation, the more stable the structure is. That said, we are interested in finding the conjugation in each structure and to what extent these sp two carbons are conjugated. If we look at structure A, we will label our double bonded carbon atoms. And what we notice is that although the six carbon atoms within the ring are conjugated, there's a separation here with an sp three carbon atom, which basically implies that structure A is only partially conjugated. It's partially conjugated because the double bond in red is separated from the conjugated system by an sp three carbon atom and green. So that is partially conjugated. Now, let's perform a similar analysis for structure B. We noticed that we have a similar scenario in which these six carbon atoms are conjugated double bonds form a pi system and similarly we have these two additional carbon atoms. So that this system is actually fully conjugated because there is no separation between the double bonded carbon atoms, they form a pi system altogether. So B is fully conjugated or completely conjugated. Now, if you look at sea, we label our double bonded carbon atoms and we noticed that we conclude the same thing. All of these carbon atoms form a conjugated system because there's no separation between any of them, all of the double bonds form a single conjugated system. So C is also fully conjugated and have a look at D for D. We label our double bonnet carbon atoms and we noticed that because there's a separation here, this is an sp three carbon atom, this is another sp three carbon atom. And here of course we have another sp three carbon atom. It's not conjugated at all because the double bonds are all separated by sp three carbon atoms, so it's not conjugated. Therefore, if we think about this problem with an increase in conjugation, the stability increases. That's what we stated previously. And if we look at our conclusions, we can conclude that because these the only one that is not conjugated at soul, that implies that D is least stable. If we have currently identified the least stable structure, we now are interested in the most stable one. The most stable structure would be mostly conjugated. If you look at B and C. They are fully conjugated. So we can immediately exclude a because it's only partially conjugated between two fully conjugated structures. We also have to recall another effect which increases stability and that that aspect is called aromatic city aromatic compounds are more stable than non aromatic ones. When we think about Elkins. So if we identify a he played in a ring and B four m plus two pi electrons according to the local school, recall that these two conditions would make the compound aromatic. I feel like that'd be. And specifically, if we look at our ring, it only has sp two carbon atoms, meaning it's plainer and it actually has four employees to pi electrons because there are a total of six pi electrons within that ring, making be aromatic. So we can include that B is also aromatic. In addition to being fully conjugated. If we look at sea, it is sufficient to notice that these are sp three carbon atoms. So essentially just sufficient to understand that this ring is not planer. It's not planer and it doesn't have four employees to pi electrons because we only see two pi electrons here within the ring system. So it's not aromatic because stability increases with aromatic city between B and c, B is more stable than C. And as a result because they're fully conjugated, but B is also an aromatic compound. B is more stable and therefore be would be the overall most stable structure. That said, we have our final answers for this problem. D Isley stable and B is most stable. And the correct answer to this multiple choice question is see if you have any questions regarding this problem. Don't hesitate to leave them down below and thank you for watching

For each set of isomers, choose the isomer that you expect to be most stable and the isomer you expect to be least stable. a.

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