Question

Which compound in the following pairs will react faster in `S_N^(2)` reaction?
(a). `CH_(3)Br` or `CH_(3)I`
(b). `(CH_(3))_(3)C Cl` or `CH_(3)Cl`

Answer 1

(a). `CH_(3)-I` will react faster than `CH_(3)-Br` because `I^(-)` ion is a better leaving group than `Br^(-)` ion. Alternatively, bond dissociation enthalpy of C-I bond is less than tthat of C-Br bond.
(b). `CH_(3)Cl` will react faster because of less steric hindrance as compared to `(CH_(3))_(3)C Cl`.