Explain the stereochemistry of $S_{N}2$ reaction with a suitable example.

In the case of optically active alkyl halides,the product formed as a result of $S_{N}2$ reaction has an inverted configuration compared to the reactant.
This occurs because the nucleophile attacks from the side opposite to the one where the halogen atom is present.
For example,when $(-)-2-$bromooctane reacts with a hydroxide ion $(OH^-)$,$(+)-$octan$-2-$ol is formed,where the $-OH$ group occupies the position opposite to the bromide ion.
The reaction is represented as:
$(-)-CH_3CH(Br)C_6H_{13} + OH^- \rightarrow (+)-CH_3CH(OH)C_6H_{13} + Br^-$.
Thus,$S_{N}2$ reactions of optically active halides are accompanied by Walden inversion (inversion of configuration).