Question

In the nucleophilic substitution reactions $\left(S_{N}2or{S}_{N}1\right)$ the reactivity of alkyl halides follows the sequence

• A. $R-I>R-Br>R-Cl>R-F$
• B. $R-Cl>R-F>R-Br>R-I$
• C. $R-F>R-Cl>R-Br>R-I$
• D. $R-I>R-F>R-Cl>R-Br$

Answer 1

Answer: (A)

Nucleophilic substitution reaction depends on leaving group ability
The correct order of reactivity is
$\text{RI}\text{>}\text{RBr}\text{>}\text{RCl}\text{>}\text{RF }$
It is due to fact, that weaker the base, better will be the leaving group.
Leaving group ability ${\text{I}}^{-}>{\text{Br}}^{-}>\text{Cl}>{\text{F}}^{-}$