Which of the following are meso compounds? Possible Answers: II only. Correct answer: I and II. Explanation : A meso compound has at least two stereocenters, but is not chiral due to an axis of symmetry. Report an Error. Example Question 82 : Stereochemistry. Which of the given chair conformations represents a meso compound? Possible Answers: I. Correct answer: III. Explanation : Meso compounds are characterized by an internal plane of symmetry that renders them achiral despite the presence of chiral center s.
Example Question 83 : Stereochemistry. Possible Answers: IV only. Correct answer: III only. Explanation : A molecule is meso if it contains at least two stereocenters, but is rendered optically inactive by internal structural symmetry.
Example Question 84 : Stereochemistry. How many possible stereoisomers does the product of the following reaction have? Possible Answers:. Correct answer:. Explanation : This is the product of the given reaction. Example Question 85 : Stereochemistry. How many of the existing configurational stereoisomers are chiral? Possible Answers: 1. Correct answer: 2. Explanation : There are three configurational stereoisomers.
Example Question 86 : Stereochemistry. How many configurational stereoisomers exist for this structure? Possible Answers: 4. Correct answer: 3. Explanation : There are two tetrahedral asymmetrical stereocenters in this molecule the carbon atoms attached to each of the chlorine atoms. Copyright Notice. I found your site while looking for tips on orgo and I have to say this is a goldmine!
I am sure you get this all the time but thank you so much for all of your help. I had just being looking at this one stereochemistry problem for the past 10 minutes and this saved me so much more time. If a molecule is chiral, is it automatically not meso? It seems like that is true from the first few sentences, but I just want to verify.
You ARE a Professor and clearly an excellent one no matter what condition academe is in. Kudos for continuing to teach and doing so accessibly vs.
Indeed a great work……. Thanks a lot for the material and that too presented in an easy way …. You are a genius. Great, that finally cleared my doubts. You explained it a gazillion times better than our chem teacher. Thanks a lot. And, they both have been singly substituted at each stereo-center. I also cannot find a plane of symmetry. How is 2A a meso compound? Further down the page I show how to do a rotation on the left-hand molecule so that you can clearly see the mirror plane.
Thanks for the info! I am a bit confused though because i thought number 2b was an enantiomer due to the r,s configuration being opposite in both. They are actually the same molecule, just rotated degrees. How to convert a Newman projections with two choral centres into a Fischer projection…..
You say that cis-1,2- dimethyl cyclohexane is meso. However, drawn as a chair, there is no plane of symmetry because one of the substituents is axial, the other equitorial. Am I understanding this correctly? Drawn as a chair, there is no plane of symmetry.
But it still is not a meso compound. The equilibrium mixture consists of interconverting enantiomers. That is why it is optically inactive, not because it is meso. You can fall into this trap with all 1,2-R,R-disubstituted even-numbered rings. In the last figure, cis 1,2-dimethylcyclohexane does not seem to have a plane of symmetry when it is drawn in chair conformation.
Can you please elaborate on this? An example would be 1,4-dimethylcyclohexane. Hence, a chiral center. Hi James! Could a 2,4 substituted molecule like 2,4 dichloropentane be meso? On the left is a model of drawing one, with the two bromines coming out at us in space. On the right is a model of drawing two, with the two bromines going away from us in space. And if I rotate the model on the right, we can see that these are mirror images of each other.
But they are superimposable mirror images. So if I put that one on top of the other, you'll see that they are superimposable. So these actually are two models of the same molecule. This is a meso compound. It's a compound that has chirality centers, but it is achiral, the mirror image is superimposable. So one and two really represent the same molecule.
This is a meso compound, a compound that has chirality centers but is achiral. The mirror image is superimposable on itself. So we thought we would have four stereoisomers, but really we only have three. We have a pair of enantiomers and we have one meso compound. So to look for a meso compound, one thing you could do is what we did in the video.
We had the mirror image and we were able to superimpose the mirror image on itself. Another way to look for a meso compound is to look for a plane of symmetry. So if I draw a line here, think about this as being a plane, and look for symmetry on either side.
So you can see, it's symmetrical. I drew in the plane of symmetry with a dashed line here, but it's hard to visualize it. So up here is a better picture. Here you can see the plane dividing the molecule in half. And on the left side, we have our bonds here and then we have our bromine going up and our hydrogen going down.
The right side is symmetrical with the left side. So look for symmetry on both sides of the plane. Let's do another example. This one's a little bit harder than the last one. We know that we have two chiral centers. So that's a chiral center and so is this one. So we would expect two to the second stereoisomer. So that's, of course, four. So I'll put a question mark here again because we're not sure if we actually will get four stereoisomers.
That's a maximum number. Down here I have the four possibilities. So I've drawn them out just to save some time. So we have one, two, three and four. And let's examine the relationship between one and two first.
On the left is stereoisomer one, and I've left the hydrogens off the methyl groups and the OH just so we can see the models better. So here's our carbon chain, and we have both OHs coming out at us in space. And then for stereoisomer two, here's the carbon chain, and we have both OHs going away from us. So I'm gonna hold them in the way they are in the drawing and I'm gonna rotate the one on the right.
And when I do that, we can see that these are mirror images of each other. But if I try to superimpose one on the other, so I'll just rotate this one back here and flip it over, you can see they don't match up. So the atoms don't line up here. So they're non-superimposable.
Doesn't matter how you do it.
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