Question

The reagent that will yield the greater amount of substitution on reaction with $C{H}_3-C{H}_2-Br$ is :

• A. $C{H}_{3}C{H}_{2}OK$ in dimethyl sulfoxide (DMSO)
• B. $(C{H}_3{)}_{3}COK$ in dimethyl sulfoxide (DMSO)
• C. Both (a) and (b) will give comparable amounts of substitution.
• D. Neither (a) nor (b) will give any amount of substitution.

Answer 1

The correct option is A $C{H}_{3}C{H}_{2}OK$ in dimethyl sulfoxide (DMSO)

For a primary alkyl halide to undergo substitution reaction, the nulceophile should be strong and smaller in size.
$\text{Nuclephilicity}\propto \frac{1}{\text{Size of}N{u}^{-}}$

$C{H}_{3}C{H}_{2}OK$ is a smaller nucleophile and the solvent is polar aprotic so it enhance the $S_{N}2$ reaction.

$(C{H}_3{)}_{3}COK$ is a larger nucleophile and the solvent is polar aprotic so it will act as strong base and gives E2 elimination product predominantly.