[Vrig]

http://www.sigmaaldrich.com/medium/structureimages/00/mfcd00064300.png

That's trans-stilben. The question is "Explain the sterochemical outcome in the bromination of trans-stilbene with Br₂. Propose a synthesis of the opposite dibromide diastereomer". I understand why we get trans-dibromide relationship when letting bromine attack nucleophilicly. I don't know how to add the two bromine syn though. Also is it possible for stilben to rotate so that we have Ph-groups cis?
Or am I not understanding the question correctly?

[curiouscat]

http://www.chemicalforums.com/index.php?topic=44068.0

[Vrig]

https://www.dropbox.com/s/9sqb841ssjwd1bp/helluu.bmp

That's the bromination of trans-stilbene, right? My question is what does "the other diastereoisomer" look like? If I'm getting this at all the bromination shown above gives us (R,S) and I think they're asking for (R,R) or (S,S)? That would mean we have to add bromine syn to trans-stilben, right? How would we do this? With oxygen we could use osmiumtetraoxide, but is there such a thing for Br? And is it possible to rotate trans-stilben or will the phenyl groups (or Br) disallow rotation because of steric hindrance?

Sorry for my poor English...!

[Vrig]

Evidently they're not stericly hindered, thus cis-stilben is possible which would give us a racemix of R,R/S,S-diastereomer and the meso compound.
You can lock the thread if you want to! Thanks