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Question
Which compound in the following pair will react faster in SN2 reaction with OH−?
(CH3)3CCl or CH3Cl
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Solution
\[\begin{array}{cc}
\phantom{......}\ce{CH3}\\
\phantom{...}|\\
\ce{CH3 - C - Cl}\\
\phantom{...}|\\
\phantom{......}\ce{CH3}\\
\end{array}\] or CH3, Cl
The SN2 mechanism involves attack by the nucleophile at the carbon bearing the leaving group. But, in the case of (CH3)3CCl, the attack of the nucleophile at the carbon atom is hindered because of the presence of bulky substituents on that carbon atom bearing the leaving group. On the other hand, there are no bulky substituents on the carbon atom bearing the leaving group in CH3Cl. Hence, CH3Cl reacts faster than (CH3)3CCl in SN2 reaction with OH−.
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OR
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\[\begin{array}{cc}\ce{CH3CH2CHCH3}\\
\phantom{.....}|\\
\phantom{......}\ce{Br}\\
\end{array}\] or \[\begin{array}{cc}\phantom{.......}\ce{CH3}\\
\phantom{...}|\\
\ce{H3C - C - Br}\\
\phantom{...}|\\
\phantom{.......}\ce{CH3}\\
\end{array}\]
