How is this compound Meso?

[skyisblue]

In my book, it says that the following compound is meso. How is it meso? Where is the internal plane of symmetry? Does it even need a plane of symmetry to be meso?

First of all, my camera sucks! But being a poor student that I am, I can not upgrade so please bear with me.

The molecule is (2R,3S)-Dibromobutane. On top we have Br on the plane of the paper, CH3 with dashed lines, and H with a wedge.

On bottom, we have H with dashed lines, CH3 with a wedge and Br with solid lines.

 

[dantheman2007]

If a compound has symmetry (as this molecule demonstrates) but has chiral carbons (as this molecule also has) it's a meso compound. If you don't see it from the picture you uploaded, you can either draw the newman projection or saw horse and convert it into a fisher.
It should be more evident from these pictures, especially once you see the fisher projection.
Hope this helps.

Best,

DantheMan2007

 

[CyborgNinjaX]

Rotate the substituents off of the C on the right. If you rotate them CW, you will see that both ends will match up with each other. There is an internal symmetry.

 

[skyisblue]

Rotate the substituents off of the C on the right. If you rotate them CW, you will see that both ends will match up with each other. There is an internal symmetry.

I didn't know you can rotate it. Thanks Cybor

 

[CyborgNinjaX]

Think of conformations. A confromation is a rotation around a bond. Rotate and you'll see symmetry.

 

[RENNOZ]

2,3-dibromobutane is a meso compound b/c

1. first there's a symmetry
2. but, not all symmetrical molecules are meso compounds. the key is that all meso symmetrical cmpd have S,R or R,S configuration. It's never S,S or R,R.

i hope that helps

 

[skyisblue]

2,3-dibromobutane is a meso compound b/c

1. first there's a symmetry
2. but, not all symmetrical molecules are meso compounds. the key is that all meso symmetrical cmpd have S,R or R,S configuration. It's never S,S or R,R.

i hope that helps

Not all symmetrical molecules are meso? What? Do you have an example?

BTW, do you guys know if in order to be meso, you must have an internal plane of symmetry?