Question

The order of reactivities of the following alkyl halides for a $S_{N}2$ reaction is

• A. RI > RBr > RCl > RF
• B. RF > RBr > RCl > RI
• C. RF > RCl > RBr > RI
• D. RCl > RBr > RF > RI

Answer 1

The correct option is A RI > RBr > RCl > RF

The reactivity of the alkyl halide in $S_{N}2$ reaction is decided by the ease with which the halide leaves the substrate. Larger the size of the halide ion, more is the leaving ability.
As per the leaving ability, the order is $I^{-}>B{r}^{-}>C{l}^{-}>F^{-}$. Hence reactivity order is RI > RBr > RCl > RF