Question

Propose a mechanism for the following reaction that explains why the configuration of the asymmetric center in the reactant is retained in the product:

Short answer

Mechanism of the given reaction

Step-by-step solution

Step-by-Step Solution Step 1: Diazotization reactions

Reactions of amines with sodium nitriles are called diazotization reactions. In these reactions, the amine group is replaced with an azo group which contains an$-\mathrm{N}\equiv \mathrm{N}$ bond. Diazotization reactions are carried out at very low temperatures as the azo group escapes as nitrogen gas into the atmosphere.

This bond is highly unstable and therefore, can be converted to a wide range of products. Therefore, diazotization is an important reaction for the synthesis of compounds from amine.

Retention and inversion of configuration

The chiral compounds are distinguished using R and S configurations. The configuration of a compound is determined by assigning priorities to the functional groups on asymmetric carbon.

The priority of a functional group depends on the atomic mass of the atom directly attached to the carbon. If the direction of the functional group from highest to lowest is clockwise, the compound is an R-isomer. If the direction is anticlockwise, it is an S-isomer.

If there is a change in the configuration of the compound in a reaction, it is called inversion. If an R reactant gives an R-product and an S-reactant gives S-product, the reaction retains the isomer configuration.

Mechanism of the given reaction

The reaction is initiated by the diazotization of the amine group by sodium nitrile. The negatively charged oxygen atom attacks the carbon in a bimolecular substitution, causing nitrogen gas removal.

The epoxide ring thus formed is broken by another bimolecular attack by the carboxyl group. This produces a five-membered ring which is the final product.

The mechanism involves two bimolecular substitution reactions causing an inversion of configuration. Since the configuration is inverted twice, the final product will have the same configuration as the reactant.

The mechanism of the reaction can be given as:

Mechanism of the given reaction