Question

Differentiate between retention and inversion.

Answer 1

Hint: When the nucleophile attacks the chiral carbon from the same side where the leaving group is present than retention of configuration is obtained. When the nucleophile attacks the chiral carbon from the opposite direction where the leaving group is present then inversion of configuration is obtained.

Complete step by step answer:

Retention	Inversion
Retention is defined as a state where absolute configuration and relative configuration of the atom or a molecule is maintained.	Inversion is defined as a state where absolute configuration and relative configuration of the atom or a molecule is not maintained. In the inversion of configuration the chiral carbon and the group attached to the chiral carbon remains change their position during the reaction to form product, that means the reactant and product does not resemble each other.
In the retention of configuration the chiral carbon and the group attached to the chiral carbon remain in the same position before and after the reaction.	Inversion is the back attack of the nucleophile takes place and in the retention front attack of nucleophile takes place.
The retention in configuration changes the R- configuration of the compound into R and S-configuration of the compound to S.	The inversion in configuration changes the R- configuration of the compound into S and S-configuration of the compound to R.

Note: The nucleophilic substitution reaction which follows the $S_{N}2$ type of mechanism shows inversion of configuration. In nucleophilic substitution reactions which follow $S_{N}1$type of mechanism, a racemic mixture is formed out of which one product shows retention in configuration and another product shows inversion of configuration.