Question

Which of the following compounds will react more rapidly by S_N2 reaction & why?

\[\begin{array}{cc}
\phantom{....}\ce{CH3}\\
\phantom{..}|\\
\ce{CH3 - C - Br}\\
\phantom{..}|\\
\phantom{....}\ce{CH3}\\
\end{array}\]

or

\[\begin{array}{cc}
\ce{CH3 - CH2 - CH - CH3}\\
\phantom{......}|\\
\phantom{.......}\ce{Br}\\
\end{array}\]

Answer 1

Tertiary halides present a steric barrier, making it challenging for the nucleophile to access the reactive carbon atom during the rate-determining stage of the S_N2 reaction. Secondary halides often have faster S_N2 reactions than tertiary halides. Therefore, 2-bromo-2methylpropane undergoes the S_N2 reaction slower than 2-bromobutane.