Which will undergo `S_(N)2` reaction fastest among the following halogen compounds?

Options

A. `CH_(3)CH_(2)F`
B. `CH_(3)CH_(2)Cl`
C. `CH_(3)CH_(2)Br`
D. `CH_(3)CH_(2)I`

Answer

D

Explanation

`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, `CH_(3)CH_(2)I` is most reactive towards `S_(N)2` reaction.