Question

Question: Draw all stereoisomers formed when each alkene is treated with mCPBA.

a.

b.

c.

Short answer

Answer

a.

b.

c.

Step-by-step solution

Epoxidation of alkene

The epoxidation of alkene is the addition of one oxygen to an alkene by forming two new C-O bonds. Epoxidation is carried out using peroxyacid, e.g., meta-Chloroperoxybenzoic acid (mCPBA)

Stereochemistry of epoxidation

The addition of oxygen to an alkene is syn (addition from the same side). Therefore, reactions are stereospecific.

Cis alkene epoxidation results in cis epoxide and trans alkene results in trans epoxide.

Reaction when alkene is treated with mCPBA

Since oxygen can be added from above as well as below the plane, two products are obtained.

When the reactant is cis, the two products obtained are diastereomers (identical or meso products)

When the reactant is trans, the two products obtained are enantiomers (non-identical and non-superimposable mirror images). The product thus is a racemic mixture.

a.

Trans reactant - enantiomeric product (racemic mixture)

b.

Cis reactant - diastereomers

c.

Trans reactant - enantiomers