Question

Which of the following will undergo a faster $S_{N}2$?

• A. I
• B. Neither I nor II
• C. Both undergo $S_{N}2$ at the same rate
• D. II

Answer 1

The correct option is D

II

For $S_{N}2$, the ideal substrates are primary or methyl halides (X = Cl, Br, I). But here we have to contend with two secondary alkyl chlorides. Observe the carbons to which the Chlorine atom is bonded. In I, the carbon to which the chlorine is bonded is immediately adjacent to a tertiary carbon which is too crowded. II is relatively unhindered sterically speaking. Hence II will undergo $S_{N}2$ at a much greater pace.