Question

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

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

Answer 1

The correct option is C

II

For $S_{N}2$, the ideal substrates are primary or methyl halides (X = Cl, Br, I). Here both are primary substrates although it is clear that the carbon to which bromine is attached in I (neopentylbromide) is adjacent to a crowded tertiary carbon. Hence II undergoes a faster $S_{N}2$.