Alkyl Halides - Result Question 22
####22. $KI$ in acetone, undergoes $S _N 2$ reaction with each $P, Q, R$ and $S$. The rates of the reaction vary as
(2013 Adv.)
P
Q
R
(a) $P>Q>R>S$
(b) $S>P>R>Q$
(c) $P>R>Q>S$
(d) $R>P>S>Q$
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Solution:
- PLAN Acetone is an aprotic solvent and can dissolve both the nucleophile and the substrate and thus $S _N 2$ reaction is favoured. Also
$$ \begin{gathered} S _N 2 \stackrel{1^{\circ}}{\stackrel{2^{\circ}}{\longleftrightarrow}} \stackrel{3^{\circ}}{\longrightarrow} \text { Alkyl halides } \ S _N 1 \end{gathered} $$
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Thus, reactivity order is $S>P>R>Q$
