Question

Increasing the concentration of an electrophile in a typical $S_{N^2}$ reaction by a factor of $3$ and the concentration of the nucleophile by a factor of $3$ will change the reaction rate to :

• A. increase by a factor of $6$
• B. increase by a factor of $9$
• C. decrease by a factor of $3$
• D. remain about the same

Answer 1

Answer: (B)

increase by a factor of $9$

$S_{N}2$ reactions follow second order kinetics. the rate is proportional to both the concnetrations of substrate and nucleophile i.e. rate = k[Rx][N$\stackrel{\ominus }{u}$]

Thus increasing the concentration of electrophile and nucleophile by 3 fold each the reaction rate increases by a factor of 9.