Are the following pairs identical, enantiomers, diastereomers,...

Question

Are the following pairs identical, enantiomers, diastereomers, or constitutional isomers?

e. Structural formulas of two chemical compounds, illustrating their relationships as isomers with specific substituents.

f. Two chemical structures with chlorine atoms, labeled

Accepted Answer

Hello everyone. Let's do this problem. It says identify whether each of the following pairs represents constitutional isomers and anti diers or identical compounds. The compounds in pair A are three chlorobutanol, they both satisfy this name. If we don't consider their configuration, we'll get into that later on in the problem. And pair B, both of the structures satisfy the name trans 14 dimethyl cyclohexane. And again, we'll get into configuration and chirality right now. So let's review these terms constitutional isomers and an tumors diers or identical compounds. How do we know what to look for when we are labeling these compounds? So, identical compounds are going to have all configurations, the same, they'll have the same atoms and the same connectivity as well. Constitutional isomers are going to have the same atoms right? Be made up of the same number of each type of atom, but they are just having a different connectivity. All right, what are in the tumors? We know they are stereo isomers and that they are non superimposable mirror images. But what does that mean for their configurations on car centers? All the configurations are going to be the opposite. So if we look at one compound and it has, let's say two carl centers on carbons one and three. And the configuration is one S3 R. The anant tumor of that compound will have the configuration one R three S. So the configuration on both chiral centers is changing. And lastly, what are ditherers? Well, these are not mirror images of one another. They are also stereo isomers and at least one configuration remains the same and at least one configuration is different. So when I say one configuration, I mean one chiral center, so again, let's consider a compound that has configuration one S3 R, the ditherer of this compound or one of the possible diers could have the orientation or the configuration one S3 S. So the configuration on carbon one is staying the same, right? One is the same and one of them is changing the one on carbon three. All right. So let's look at our compounds now that we know what these terms mean and let's identify their relationship. So we already mentioned that these both of these compounds in pair A satisfy the name three Chloro Butan two. All right. So they're not gonna be constitutional isomers, right? They are not going to be constitutional isomers because they have the same connectivity. So they're either going to be identical and an tumors or diers. So we can check the configuration on these two chiral carbons, but we don't necessarily have to assign S or R configuration here since we're not naming the compound, right. That's not the goal, I'll show you a little shortcut on how to determine whether or not the configurations are the same without assigning R or S configuration. So you can simply look at the order of the groups attached to the compound. So I'll show you what I mean by that on the first compound on the carbon with the methyl group, hydrogen and chlorine, let's start at the top from the methyl group. And I'm going to go clockwise in a circle and I'm going to list the groups that in the order that they appear. So we have the methyl group, I'll just write c then we have C L, then we have hydrogen. OK. Now what about our second compound? Same carbon, same groups is the order the same. So start with the same group and go in the same direction. So we went clockwise. So we'll go clockwise. And now what is the order that the groups appear in carbon or methyl hydrogen chlorine? Now you ask yourself, is this order the same or different? If it's the same, then they have the same configuration. If it's different, then they have different configuration. So they are different, right? The order for the first compound goes methyl chlorine hydrogen, the second compound, it goes methyl, hydrogen chlorine. So the configuration is changing on that first carbon. All right, let's check the second carbon will do the same thing, starting with the alcohol group, we'll go clockwise again, but make sure you're considering the 3d space, right? So if this alcohol is dash and if we go clockwise, then that would bring us down to the methyl and then up to the hydrogen in the front. So we have alcohol methyl hydrogen. And if we do the same for the second compound, starting with the same group, it's easiest to identify the differences if you start with the same group and then you wanna go in the same direction. So clockwise. So starting with the alcohol, considering their space, we would end up at the methyl first and then back at the hydrogen. So we go alcohol methyl hydrogen. So is the orientation on this second chiro carbon the same or different. It's the same, right? We go alcohol carbon hydrogen, alcohol carbon hydrogen. So one carl center is changing configuration, the other one is staying the same. So these are dier. Isn't that cool? We didn't even have to assign priorities to any of the groups, right? So that's my little shortcut, moving on to pair B. All right, we said both of these compounds satisfy the name trans 14 dimethyl cyclohexane, right? We have cyclohexane di substituted with two methyl groups on carbons, one and four and the groups are on opposite sides of the ring, right? We have one methyl group on the top face of the ring, one methyl group on the bottom face of the ring. But if you recall Johnny's test three for stereo chemistry, which is about di substituted cyclo ALCA. You'll recall that a 14 pera die substituted cyclo ALCA, just like we have here is always going to be a chiro, right? They are the same group and they are going to have a plane of symmetry or a line of symmetry right down the center of the structure. So these are a chiral. So therefore, we can't have anant tumors or diers. They are going to be identical compounds and it doesn't matter whether they are sis or trans, if they are parady substituted right in the position. So to recap, pair A are diers and pair B are identical compounds. That's it for this problem. I hope this video is helpful and thanks for watching.

Are the following pairs identical, enantiomers, diastereomers, or constitutional isomers?
e.
f.

Key Concepts

Stereoisomers

Enantiomers

Diastereomers

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