Question

Which of the following compounds will react faster?

${CH}_3{CH}_{2}Br$ or ${CH}_3{CH}_{2}I$ with $NaOH$ in acetone.

• A. ${CH}_3{CH}_{2}I>{CH}_3{CH}_{2}Br$
• B. ${CH}_3{CH}_{2}I<{CH}_3{CH}_{2}Br$
• C. ${CH}_3{CH}_{2}I={CH}_3{CH}_{2}Br$
• D. None of these

Answer 1

Answer: (A)

${CH}_3{CH}_{2}I>{CH}_3{CH}_{2}Br$

While acetone is polar and dissolves a number of polar reactants used in

nucleophilic substitution reactions, it is not nucleophilic. For this reason, it is frequently used as a solvent in $S_{N}2$ reactions. Chloroalkanes $(R-Cl)$ react more slowly than bromoalkanes $(R-Br)$. These relative reaction rates have the same order as the relative strengths of the $C-X$ bonds. The reaction rate of $S{N}_2$ reactions of $R-X$ decrease in the order $R-I>R-Br>R-Cl>>>R-F$.