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}$
