Now isomers are molecules with same molecular formula but different connectivity or spatial orientation. Here, the two types of isomers we can delve into are structural or constitutional isomers. These have the same molecular formula but different connectivity. And then stereo isomers, these have the same molecular formula and connectivity but different spatial orientation. So what exactly do we mean by this? Well, if we take a look at this middle compound, we have as its formula C 4h 8. Now only co mean structural or constitutional isomers, that means we have the same four carbons but they're connected differently to one another. In this example, we have the four of them forming a chain. But what I could do here is have three of them forming a chain. And then that fourth one branching off of that middle one, we also need to include the double bond. So I decided to make a double bond between these two carbons. This would represent one possible structural isomer of this middle compound. They have the same molecular formula of C 4h 8 but their connections or connectivities are definitely different. Now stereo isomer, what do we mean by that? Well, they have the same molecular formula and connectivity. So we'd still have our four carbons in a chain, but they have different spatial orientation. These two carbons in the middle would still be double bonded. But now I have one of these carbons pointing up and one of them pointing down, this would represent a different spatial orientation because in our original compound, both of these carbons are pointing up by making them opposites of each other. Now, this represents its stereo isomer, right. So just remember when it comes to isomers, we have two big categories of structural A K A constitutional isomers and then stereo isomers.
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concept
Stereoisomers
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Stereo isomers themselves are further divided into two types. We have our geometric stereo isomers and our optical stereo isomers with geometric stereo isomers. These are molecules with different spatial arrangements around a double bond optical isomers. On the other hand, these are molecules that are non super super imposable mirror images of each other. Now when we say non super imposible, these mirror images cannot be placed one over the other. So just imagine you have a dog and this dog is looking into a mirror, this mirror image of itself would mean that these two dogs are optical stereo isomers. If we were to take this dog and take it out of the mirror and try to slide it over this dog here, we would see that they don't perfectly line up because if you slit it all the way over to the left, we have this spot here. So when you, when you slide it over, it would appear over here, but that doesn't match up with this dog where the spot is on this side. Now this and this would more or less match up with this and this but again, it's this portion here. When you slide it over the other dog that would not match up. That makes these two optical stereo isomers of each other. And remember the fastest way to look at it is to look at two molecules. Imagine there's a mirror between them. The molecule on the left when it looks into the mirror, does it see the molecule on the right? If it does, that means there are optical stereo isomers of each other. That's the easiest way to understand this type of stereo isomer. Now that we've talked about these two additional types of stereo isomers. Click on the next video and let's take a look at an overall chart.
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concept
Types of Isomers
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So here we're taking an overall look at the different types of isomers that exist. So remember, structural isomers have the same molecular formula but different connectivity in both of these image, we have C four, 10, four carbons, 10 hydrogens. The one on the left has them all oriented in a chain. But the one on the right has three of them in a chain and one branching group. So they're connected differently, but they still have the same molecular formula of H 10 or C 4h 10. On the other side, we're looking at stereo isomers which we just learned can be further divided into geometric and optical isomers. Here in the geometric one, we're able to tell that they're geometric isomers by the inclusion of a double bond. Now, if we're looking at the double bond, we see we have these two ch three groups on the same side with each other. And then here we have them on opposite sides of each other. Later on, we'll learn that when they're on the same side, these two groups, they are sis and then when we have two groups opposite each other, they're called trans optical isomers. The way we are able to tell we have optical isomers is just imagine you're looking into a mirror, looking into a mirror, we see the inversion of ourselves. But another way we can show that we have an optical isomer is we look at the bonds that shows spatial orientation instead of looking into a mirror. If we looked into a mirror, what we would see would be the same molecule, but this is looking into a mirror. So oh will be over here and then this age would be back here. And this ch three would be here. That would be our mirror image. Sometimes it's hard to depict that because you're moving things and orienting them a different way. An easier approach would just be to look at the bonds that have spatial orientation and invert them. So here this is a dashed wedged bond. We change it to a solid wedged bond. This is a solid wedge bond which hated to a dashed wedged bond doing it this way by inverting the bonds with that show actual spatial orientation and holding everything else in the same position. This actually becomes its optical isomer. This is its mirror image. OK. So again, you can look into a mirror and actually draw this which is a bit trickier, we can just invert the bonds that are uh solid or dashed right. So these are the different types of isomers that exist. Remember, isomers here have the same molecular formula but they may have the same connectivity or spatial orientation or different connectivity and spatial orientation. Depending on what happens you can fit under structural isomers or stereo isomers.
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example
Isomers Example
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Based on the pair of molecules identify a structural optical geometric isomers or identical. So if we take a look here at the first one, we have bonds that have spatial orientation, usually this is a key to give away that we're dealing with optical isomers. Now, if we imagine that this is looking into a mirror, it would see its reflection back the would be looking this way which it is the CH three would be looking this way which it is, we'd have our BR here and looking in the mirror, the oh would be here in the back. So this is the mirror image of this original one here on the left. So they are optical isomers. For the next one, we have the presence of a double bond, which usually indicates that we have a geometric isomer. But we have to check in this one. Both CLS are on the same side and on this one, both seals are still on the same side. Now, they're not geometric isomers for them to be geometric isomers, we'd have to have one where the CLS are on different sides. Both are saying the same thing. So they represent identical molecules for the next one. What do we have here? So we have this structure here and we have this structure here. If we look, what do we see? We see that we have what we have this chain here and branching off of it? Is this oh I mean this uh ch three and this oh And then what else do we have? We have this chain here which has four carbons as well. And coming off of it is this CH two. And then here oh H it's better to draw it this way to show the actual connection to the o. So if you look, they both would have the same number of carbons, hydrogens and oxygen, but they look like they're connected differently. So here we say that these are structural isomers, OK. Same molecular formula but different connectivity. So this is how we classify each one of these three options.
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Problem
Problem
Examine the two molecules and determine if they are identical or isomers.