What is the Relationship Between Isomers? - Video Tutorials & Practice Problems
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One of the most frequently asked exam questions in this chapter is:“What is the relationship between the following two molecules?”. We’re going to learn a systematic method to solve these questions.
1
concept
Different atoms or different connectivity.
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1m
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Video transcript
All right, So now we're gonna talk about one of the most important types of problems that you guys are gonna get in this chapter, and it has to do with identifying the relationship between two different types of ice occurs. All right, so maybe you guys remember this flow chart? I made it. When you're talking about constitutionalism. Er's remember that we talked about how the very first step is to verify that all the atoms of the same so we would count the non hydrogen atoms and the HD in both compounds. We've said if they were not exactly the same thing, they were different compounds, okay? And then we said that if they were the same, then you would go to step two and then we would talk about connectivity. When we said, Are they all connected the same. We talked about that. You look for a landmark, Adam. Okay, this is all review. Based on what we learned from constitutionalism er's. And then we said, if they're not exactly connected the same, then they're constitutionalism er's. And then we said if they were, we said back then we said that if they had the same atoms And if they were connected the same, then we were going to say that they were identical. Okay, So usually for the when we're talking about constitutional items, we would have put identical in this blank. But it turns out that now that we have the possibility of stereo I summers, we actually have to go to step three now. Okay, instead of just assuming that they're identical, No, we have to look at the stereo customers. You would have to say. Stereo centers you have to say, is this and our is this an S stuff like that?
2
concept
Same atoms, same connectivity, 0 chiral centers.
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37s
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Video transcript
So now we have to go to Step three. And what steps three talks about is Cairo centers and tribunal centers. So let's go ahead and go for this. So now that we verified that all the atoms of the same and the connectivity is the same, now we're going to talk. Look for Cairo centers. So if we have basically, if we have zero Cairo or tribunal centers present Okay, so that means all the items, the same connectivity is the same. And there's zero Cairo or tribunal centers in the two molecules are identical. Okay, so this is that blank that we would have used earlier when you would have said identical. But now we're just verifying that there's no Kyle centers of tribunal centers.
3
concept
Same atoms, same connectivity, 1 chiral center.
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1m
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But what if you do have one Cairo center, which happens all the time? Okay, Well, if you have the same Cairo center on both, then they're identical. Okay, if you have different Cairo centers for both than the relationship is gonna be in anti Amer's. Okay? And let me illustrate this with the following molecules. Let's say that I have two beautiful and I have another two. Beautiful. Okay, so I've already verified that these two compounds have the same molecular formula. They have the same I HD everything and they have the same connectivity. They're both secondary alcohols. That air butin als. Alright, So then I go ahead and I figure out the configuration of this and I figure out that this one is our as one Carl center, and this one is also our So what do you think that relationship is? Well, that's gonna be identical. Okay? Because they're the same molecule on. They have the same Cairo center. Okay, Now, what if I'm comparing it to instead of are what if I were comparing it to the same molecule, but now my o h is on a dash. Okay. Now, instead of being are this one's gonna be s okay. What do you think is the relationship between these two guys? Okay, well, we have one Cairo center and they're different. So then these would be in the anti MERS or mere images. Does that make sense? That's the way this flow chart works. Basically, we look step by step, you say. Are they the same? Are they different, etcetera?
4
concept
Same atoms, same connectivity, 2 or more chiral centers.
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2m
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Video transcript
So let's go on to if we have to arm or Cairo centers. Okay, If we have two or more Cairo centers and all of them are identical, all of them are exactly the same. Then the molecules are still gonna be identical. Okay, So, for example, if I have a molecule that's three Cairo centers and the Carl centers are like this, let's say it's to our three are and then five s. Okay? And then I'm comparing it to another molecule that has the same molecular formula. Same connectivity, and it happens to be to our three are and five s as well. Okay, then those were gonna be identical. Okay, How about if all of them are exactly the same? Exactly different. So what if I was comparing it to To S three s five are. Okay, then what would that relationship be? Well, here, what we see is that every single one is opposite. Every single Carl center has flipped, has switched. So because of that, this would be the mere image. So if they're all different, that's gonna be an anti MERS as well. Okay. And we've already talked about this a little bit when I talk to you guys about the different types of stereo customers you could have, Then if everything is completely different, that's in AnAnd Teamer. Okay, but what if not all of them are different? But not all of them are the same. So what if we have this middle situation where I have to? Our three are, and then I have five are. Okay, so now I have two of them. There are the same, but I have one of them that's different. Okay, what kind of situation would that be? Well, that would be right in the middle, where it's not the same. It's not different. It's not gonna be a mirror image, but it's still different. So this is a diet steri. Um, okay. And that's the way we think. If there kind of different but kind of the same, that would be a die of stereo. Does that make sense? Guys
5
concept
Same atoms, same connectivity, 1 or more trigonal centers.
Video duration:
2m
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Video transcript
So let's go to a few more, and then we'll be done. How about if we have to Cairo centers that are symmetrical and opposite to each other? This is a special case. We have to Carl centers that air symmetrical on opposite to each other. That's gonna be me. So compounds. Okay? Remember we discussed that missile compounds were kind of an exception where they have to carl centers, but they cancel out because they're opposite. Okay, Awesome. So those would be Nestle Compounds. And then finally, we've been talking about Cairo centers. What about tribunal centers? Lett's kind of its own thing. So for tribunal centers, if I have one or more tribunal center and both of them are the same, then that's gonna be identical. Okay, So an example of that would be too beauty. Mean versus to beauty. Okay, notice that I'm pitting. I'm doing assists and assists on I'm comparing them. If they both have the same arrangement, Sister Trans, then they're just gonna be identical. But what if I'm comparing it to that one versus the trans? Okay? Versus Trans Tube, You teen. Okay, what's that relationship gonna be? And it turns out that these air Definitely. Stereo y summers, right? They look different, but they're not mirror images. One is not the mirror image of the other. So these air actually gonna be dia stereo MERS? Okay. And that is always the case. When you have double bonds that switch system trans, you're always gonna get dia stereo MERS as a product, not any anti more. So don't think of any answers, because the Nancy Meyers are mirror images. But the's basically this one here and this one up here are definitely not mirror images of each other. So they're dying stereo MERS that the relationship does that make sense. Cool. So I want to teach you guys a little secret here. Okay, I've given you all these rules. This is your flow chart. I really want you guys toe Use this a lot. Apply it to memory. And also just use it as when you're doing your practice problems. Have this out for reference.
6
concept
When to use R and S, when you don’t have to.
Video duration:
1m
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Video transcript
something that's gonna help is that this whole time I've been comparing s and are so that implies that every single time you have to figure out our n s okay, But it turns out that the same and the different part can actually work without finding R N s. So, for example, if I had a molecule that you know, if I have two molecules, I was gonna draw something, But I think I'll just explain it. If I have two molecules that look exactly the same except that the wedges and dashes air different, I don't need to actually calculate system R and S. I could just instead say, Are they the same or different? Okay, But that Onley works if my molecules haven't been rotated. If my molecules are rotated meaning that your molecules are rotated into different positions when you're comparing them, then you actually do have to figure out our n s. Okay, so what I'm trying to say here is that r and s if you figure that out, you always get it right. That's always the failed way fail proof way to do it. But a lot of times we're gonna cheat and instead of using our N s, we're just gonna look and say, Hey, are the molecules rotated? No, they're exactly the same position. The only thing that's changed is the bond Is the bond being towards the front of the back? And in that case, I would just say, Are they the same or they different? And that's going to save me a lot of time. Alright. So with that said, let's go ahead and move on to the next page and see if we could figure out these relationships.
Solving for R and S on every single molecule can be a headache. If the molecule hasn’t been rotated, feel free to use “different or same” as a surrogate for R and S (we’ll practice this so you see what I mean).
7
Problem
Problem
Identify the relationship between the following organic compounds:
A
Constitutional Isomers
B
Diastereomers
C
Enantiomers
D
Identical
8
Problem
Problem
Identify the relationship between the following organic compounds:
A
Constitutional Isomers
B
Diastereomers
C
Enantiomers
D
Identical
9
Problem
Problem
Identify the relationship between the following organic compounds:
A
Constitutional Isomers
B
Diastereomers
C
Enantiomers
D
Identical
10
Problem
Problem
Identify the relationship between the following organic compounds: