Question

Choose the correct statement for the given $S_{N}2$ reaction.

• A. $F$ gets replaced, S is absolute configuration of product
• B. $Br$ gets replaced, R is absolute configuration of product
• C. $Br$ gets replaced, S is absolute configuration of product
• D. $F$ gets replaced, R is absolute configuration of product

Answer 1

The correct option is C $Br$ gets replaced, S is absolute configuration of product

$Br$ is better leaving group than $F$ due to the weak $C-Br$ bond compare to $C-F$ bond.
This is an example of $S_{N}2$ reaction which is a one-step reaction which takes place via the formation of transition state.
Generally it will give inversion in configuration but here the priority of the groups of the reactant and product are different. Thus, by following the reaction via $S_{N}2$ mechanism, the product give same S configuration as the substrate.