For which of the following leaving groups, X , will the S _ N 2 reaction shown below proceed most rapidly?

Step-by-step solution

The given reaction is an S _ N 2 substitution where SH ⁻ acts as a nucleophile and X ⁻ acts as a leaving group. The rate of an S _ N 2 reaction increases with the leaving group ability of X . A good leaving group is a weak conjugate base. The conjugate acids of the given leaving groups are HBr , HI , H ₂ O , and HCl . The acidic strength order of these conjugate acids is: HI > HBr > HCl > H ₂ O Therefore, the basic strength order of the corresponding anions is: I ⁻ Since I ⁻ is the weakest base, it is the most stab