Question

We performed a bromination of trans-stilbene in lab (A green chemistry experiment).

Suppose that you perform the same reaction under different conditions (in which a different mechanism operates), and you end up with a product that is a mixture of (R,S), (R,R), and (S,S).

Which purification technique could be used to isolate the (R,S) compound from the other two stereoisomers? Explain why this technique would be successful.

Why can the (R,S) isomer be separated from the other two? Explain your answer.

Can the (R,R) isomer be separated from the (S,S) isomer using any technique? Why or why not?

Answer 1

1. Diastereomers have different physical properties like Melting or Boiling Point etc.

(R,S) isomer is having diastereomeric relationship with (R,R) and (S,S).

It means (R,S) isomer have different M.P and B.P. than (R,R) & (S,S). And being having different M.P. and BP we ca separate it from (R,R) & (S,S).

2. (R,R) and (S,S) forms an enantiomeric pair. Enantiomers have almost same physical & Chemical Properties in non chiral environment.

Enantiomers have different chemical properties in chiral solvent and different one of the enantiomer pair react differently than other. May one of the enantiomer react and other do not t all.

This is called Chiral separation.

Using Chiral separation technique we can separate enantiomes (R,R) and (S,S).

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