Question

Which will undergo $S_{N}2$ reaction fastest among the following halogen compounds?

• A. $C{H}_{3}C{H}_{2}F$
• B. $C{H}_{3}C{H}_{2}Cl$
• C. $C{H}_{3}C{H}_{2}Br$
• D. $C{H}_{3}C{H}_{2}I$
• E. ${\left(C{H}_3\right)}_{2}CH-Cl$

Answer 1

The correct option is D $C{H}_{3}C{H}_{2}I$

$S_{N}2$ reactions involve the formation of intermediate transition state, thus less hindered alkyl halide readily undergoes $S_{N}2$ reaction.
Moreover, $C-I$ bond is less stable than $C-Br$ or $C-Cl$ bond, thus alkyl iodides are more reactive as compared to other halides.
Hence, $C{H}_{3}C{H}_{2}I$ is most reactive towards $S_{N}2$ reaction.