Question

Sort out following halogens in decreasing order of their leaving capacity in $S_{N}2$ reaction

• A. $F$
• B. $Br$
• C. $I$
• D. $Cl$

Answer 1

A good leaving group is conjugate base of strong acid. The acidic strength of the given acids can be given as:
$HI>HBr>HCl>HF$
So, the the order for leaving group will be:
$I^{-}>B{r}^{-}>C{l}^{-}>F^{-}$