d
\(\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,\,\,C{H_3}} \\ 
  | 
\end{array}\,\,\,\,\,\,} \\ 
  {{H_3}C - C - C{H_2}Br} \\ 
  {|\,\,\,\,\,\,} \\ 
  {H\,\,\,\,\,\,} 
\end{array}\) \({\mathop{\xrightarrow{C{{H}_{3}}{{O}^{-}}}}}\,A\)

Alkyl halide is  \(1^o\)

Keep in mind \(1^o\) halide give product by \({S_{{N^2}}}\)/ \(E‌‌‌_2\)  mechanism and \( 1^o\)  halide always gives substitution reaction except when strongly hindered base is used.

ex.: With \(\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,C{H_3}} \\ 
  {\,\,\,\,|} 
\end{array}\,\,\,\,\,\,} \\ 
  {C{H_3} - C - O\,( - )} \\ 
  {\,\,\,|\,\,\,\,\,\,} \\ 
  {\,\,\,\,\,\,\,\,\,\,C{H_3}\,\,\,\,\,\,} 
\end{array}\) it gives mainly elimination.

The reaction involves carbocation intermediate.

i.e. \(\mathop {\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,C{H_3}} \\ 
  {|\,} 
\end{array}} \\ 
  {C{H_3} - C - \mathop C\limits^ \oplus  {H_3}} \\ 
  {|\,} \\ 
  {H\,} 
\end{array}}\limits_{\left( {primary{\text{ }}carbocation} \right)} \)

but as it is a primary carbocation it will rearrange to give a tertiary carbocation, which completes the reaction

\(\mathop {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,C{H_3}} \\ 
  \,\,\,\,\,\,\,| 
\end{array}} \\ 
  {C{H_3} - {C^ \oplus }} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} 
\end{array}}\limits_{teritiary{\text{ }}carbocation} \)

Stability of carbocation : \(3^o > 2^o > 1^o > \) \(\mathop C\limits^ \oplus {H_3}\)

It is because the stability of a charged system is increased by dispersal of the charge. The more stable the carbocation, the faster it is formed.

\(N.B.\) -Rearrangement can be done in two ways.

\(\begin{array}{*{20}{c}}
  {\,\,C{H_3}} \\ 
  {\,\,|\,\,\,\,} \\ 
  {C{H_3} - C - \mathop {{\text{ }}C}\limits^ \oplus  {H_2}} \\ 
  {|\,\,\,} \\ 
  {H\,\,\,} 
\end{array}\) \(\xrightarrow{{H\, - \,shift}}\) \(\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,C{H_3}} \\ 
  | \\ 
  {\mathop {C{H_3} - \mathop {{\text{ }}C}\limits_ \oplus   - C{H_3}}\limits_{(teritary\,\,\,carbocation)} } \\
  {{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} } 
\end{array}\)

\(\begin{array}{*{20}{c}}
  {\,\,C{H_3}} \\ 
  {\,\,|\,\,\,\,} \\ 
  {C{H_3} - C - \mathop {{\text{ }}C}\limits^ \oplus  {H_2}} \\ 
  {|\,\,\,} \\ 
  {H\,\,\,} 
\end{array}\) \(\xrightarrow{{CH_3\, - \,shift}}\) \(\mathop {\begin{array}{*{20}{c}}
  {C{H_3} - \mathop {{\text{ }}C}\limits^ \oplus   - C{H_2} + Br} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {H\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}}\limits_{{\kern 1pt} {\kern 1pt} (secondary\,\,carbocation)} \)

\(\begin{array}{*{20}{c}}
  {C{H_3}\,\,\,\,\,\,\,\,} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {C{H_3} - C - C{H_2} - Br} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}\)\( = \begin{array}{*{20}{c}}
  {C{H_3}\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {C{H_3} - C - CH_2^ \oplus  + B{r^ - }} \\ 
  {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ 
  {H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} 
\end{array}\)\( \longleftrightarrow \begin{array}{*{20}{c}}
  {\,\,\,\,\,\,C{H_3}} \\ 
  | \\ 
  {C{H_3} - \mathop {{\text{ }}C}\limits_ \oplus   - C{H_3}} 
\end{array}\xrightarrow[{C{H_3}OH}]{{C{H_3}{O^ - }}}\)\(\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,C{H_3}} \\ 
  | \\ 
  {C{H_3} - C - C{H_3}} \\ 
  | \\ 
  {\,\,\,\,\,\,\,\,\,OC{H_3}} 
\end{array}\)