Question

A nucleophilic substitution reaction can occur via $S_{N}1$ and $S_{N}2$ mechanism. The ease of the reaction to go through $S_{N}1$ or $S_{N}2$ depends upon many factors. Ionisation has an important role to play in such reaction. The process of ionisation initially generates a carbocation and a counter ion in proximity to each other. This species is called an initimate-ion pair. This species can proceed to a solvent seperated ion pair, in which one or more solvent molecules have inserted between the carbocation and the leaving group. Then diffusion of ions occurs.
What would be the expected stereochemistry of the product if a coming nucleophile attacks on carbocation at intimate-ion pair stage.

• A. Inversion
• B. Racemisation
• C. Retention
• D. No reaction will occur at intimate-ion pair stage

Answer 1

The correct option is C Retention

At intimate-ion pair stage attack of a nucleophile can occur with inversion of configuration since the leaving group would still shield the front side of the carbocation.