Meso Compounds - Don't Quite Get it

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skyisblue

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As I continue to read up on meso compounds, the more I get confused. By definition, a meso compound is a compound that is achiral even though it contains chirality centers. One quick way to determine if it's a meso compound is if it has a plane of symmetry. Okay, I get that, but here is where I get confused......

trans-2-butene + Br2 produces (2S,3R)-Dibromobutane (meso) and (2R,3S)-Dibromobutane (meso).

Upon close inspection, the products are suppose to be identical. BUT, are they really identical when the configurations at each chirality center is different?? How is 2S the same as 2R?? And 3S the same as 3R?? And with these products, where is the plane of symmetry drawn??

I don't get it...
 

blue_moon01

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So, we don't really need to look at the configurations at the individual chirality centers?? Are meso compounds basically compounds that are identical???

Help!

Meso compounds have chiral centers but are not optically active because it's superimposible on it's mirror images.

1) draw the molecules out and if there's a plane of symmetry then.. :) you know this rule already

2) draw the molecules and rotate one according to the fischer projection.. if you can superimpose one on the other.. you've got yourself a meso compound

The two molecules listed above in your post.... When you draw them out and rotate them you'll see that they are identical

Basically, you need to draw them out and rotate them.... once you get the hang of it ... you'll be able tell meso or not really quickly.
 

skyisblue

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Meso compounds have chiral centers but are not optically active because it's superimposible on it's mirror images.

1) draw the molecules out and if there's a plane of symmetry then.. :) you know this rule already

2) draw the molecules and rotate one according to the fischer projection.. if you can superimpose one on the other.. you've got yourself a meso compound

The two molecules listed above in your post.... When you draw them out and rotate them you'll see that they are identical

Basically, you need to draw them out and rotate them.... once you get the hang of it ... you'll be able tell meso or not really quickly.

Can you rotate it in any way? Out of the plane, in the plane etc.??
 

skyisblue

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When are you taking your DAT? I will be taking mine over the summer July or August.:scared: Still rusty on the reading comp. You have anytips for this section?

I want to take the DAT asap. I even wanted to take it last month. As for the RC section, I say practice practice practice! You'll figure out as you go what is your best method.
 
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