Stereochemistry of SN₂ reaction involves:  

CONCEPT:

Stereochemistry of SN2 Reactions

• SN2 Reaction Mechanism: The SN2 (bimolecular nucleophilic substitution) reaction involves a single-step mechanism where the nucleophile attacks the electrophilic carbon from the side opposite to the leaving group, leading to the formation of a transition state and then the product.
• Backside Attack: Since the nucleophile attacks from the side opposite to the leaving group, a backside attack occurs, which flips the configuration of the carbon center.
• Stereochemical Outcome: The SN2 reaction leads to an inversion of configuration at the chiral center, also known as "Walden inversion".

EXPLANATION:

• In an SN2 reaction, if the reactant molecule has a chiral center, the reaction will result in an inversion of the configuration at that chiral center.
• This inversion happens because the nucleophile must approach from the side opposite to the leaving group, effectively flipping the spatial arrangement of the substituents around the chiral carbon.
• 
• This process is different from racemization (which produces a 50:50 mixture of both enantiomers) and retention (which maintains the original configuration).

The correct option is 2) Inversion.