Question

Question: a. Which diastereomer of oct-4-ene yields a mixture of two enantiomers, (4R,5R)- and (4S,5S)-4,5-dibromooctane on reaction with Br₂ ?

b. Which diastereomer of oct-4-ene yields a single meso compound, (4R,5S)-4,5-dibromooctane?

Short answer

Answer

a.cis-4-octene

b.trans-4-octene

Step-by-step solution

Diastereomer  

The diastereomers are cis and trans forms of an alkene. Bromination enables anti-addition which gives enantiomers.

Bromination on the trans form gives only the meso compound.

Explanation

The diastereomer of oct-4-ene is cis-oct-4-ene. The reaction of cis-oct-4-ene with proceeds by anti-addition, which ultimately gives enantiomers by changing the stereochemistry.

Enantiomers

The diastereomer of oct-4-ene is trans-oct-4-ene. The reaction of trans-oct-4-ene with Br₂ proceeds by anti-addition, which ultimately gives the meso product due to the presence of a plane of symmetry.

Meso compound