Question

(a) Draw the structure of major monohalo products in each of the reaction.(refer diagram)
(b) Which halogen compound in each of the following pairs will react faster in $S_{N}2$ reaction:
(i) $C{H}_{3}Br$ or $C{H}_{3}I$
(ii) ${\left(C{H}_3\right)}_{3}C-Cl$ or $C{H}_3-Cl$

Answer 1

(b)

(i) $C{H}_{3}I$ will react faster in $S_{N}2$ reaction than $C{H}_{3}Br$. This is because $I^{-}$ is a better leaving group, owing to its greater size than $B{r}^{-}$. As a result, it will leave at a faster rate in the presence of an incoming nucleophile.

(ii) $C{H}_{3}Cl$ will react faster in $S_{N}2$ reaction than $(C{H}_3{)}_3-Cl$, as $C{H}_3-Cl$ is a primary halide whereas $(C{H}_3{)}_{3}C-Cl$ is a tertiary halide. Primary halides undergo $S_{N}2$ reactions faster.