Q11P - Organic Chemistry (Mcmurry)

Question

Reaction of cis-2-butene with m-chloroperoxybenzoic acid yields an epoxide different from that obtained by reaction of the trans isomer. Explain.

Step-by-Step Solution

Answer

Answer

The reaction of cis-2-butene and trans-2-Butene with m-chloroperoxybenzoic acid is, 

Step-by-Step Solution Step 1: Alkene on reaction with peroxyacid

The alkene reacts with peroxyacid in a one-step and produces epoxide. The most commonly used peroxyacid is MCPBA (m-chloroperoxybenzoic acid). The cis-isomer forms cis product, and the trans isomer forms a mixture of enantiomers of trans product.

Step 2: The reaction of cis-2-Butene with m-chloroperoxybenzoic acid

There is a syn addition of oxygen to a double bond when epoxidation is done using m-chloroperoxybenzoic acid (RCO₃H). The original bond stereochemistry is retained, and the product obtained is a meso compound. When alkene is a starting material, the methyl groups are cis in the epoxide product.

                                    Formation of cis product

Step 3: The reaction of trans-2-Butene with m-chloroperoxybenzoic acid

A trans product is obtained when trans-2-Butene reacts with m-chloroperoxybenzoic acid. The peroxyacid can attack either from the top or bottom of a double bond, forming a mixture of enantiomers.

                                        Formation of trans product