Question
Question: mcPBA \(\to\) meta-chloro perbenzoic acid.  Meso
(b) Racemic
(c) Diastereomers
(d) Optically inactive due to absence of chiral center.
Solution
mcPBA is useful reagent which is used in organic chemistry for the synthesis of epoxides from alkenes. The addition of oxygen takes place to the double bond of alkene.
Complete step by step answer:
The reaction between an alkene and mcPBA is called an epoxidation reaction. The epoxidation reaction is also termed as oxygen insertion reaction.
mcPBA is known as meta-chloro perbenzoic acid or meta-chloroperoxybenzoic acid. It contains a peroxide linkage. It is a stable peracid and the oxygen attached to the carboxylic group is electron deficient oxygen or electrophilic. It attacks the electron rich alkene and the reaction proceeds through a concerted transition state.
The mechanism for the reaction is shown as
The addition of oxygen atom to the alkene results in the generation of chiral center marked as (*). Thus the compound is optically inactive due to formation of a racemic compound.
Before going into the answer of the question let us understand the given options one by one. Meso compounds are achiral compounds which contain two or more stereogenic centers. The compounds are superimposable mirror images of each other.
Racemic compounds are the compounds which contain equal amounts of both the enantiomers. Diastereomers are pairs of isomers which are not mirror images of one another.
The given alkene is a mono substituted alkene. The addition of an alkene will generate a chiral center. As a result the reaction gives an equal mixture of enantiomers which is called a racemic mixture. The product of the reaction is shown as
Hence the stereochemistry of the product of the given reaction is racemic.
option (b) is the correct answer.
Note: The epoxidation reaction is a useful reaction in organic chemistry for the generation of chiral centers. Reaction of unsymmetrical polysubstituted alkenes leads to generation of both pair of enantiomers and diastereomers.