→ There are three outcomes for a reaction at an asymmetric carbon atom, when a bond directly linked to an asymmetric carbon atom is broken.
→ Consider the replacement of a group X by Y in the following reaction;

→ If (A) is the only compound obtained, the process is called retention of configuration.
→ If (B) is the only compound obtained, the process is called inversion of configuration. Configuration has been inverted in B.
→ If a 50:50 mixture of A and B is obtained then the process is called racemisation.
→ The product is optically inactive, as one isomer will rotate the plane polarised light in the direction opposite to another.