MCQ
Stability order of following carbocation is :

$(i)$ $\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}-CH_2} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,|} 
\end{array}} \\ 
  {C{H_3} - {C^ + }} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} 
\end{array}$

$(ii)$  $\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,|} 
\end{array}} \\ 
  {C{H_3} - {C^ + }} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{H}} 
\end{array}$

$(iii)$ $\begin{array}{*{20}{c}}
  {\begin{array}{*{20}{c}}
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,|} 
\end{array}} \\ 
  {C{H_3} - {C^ + }} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ 
  {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} 
\end{array}$

$(iv)$ $Ph - CH ^{+}-\underline{ CH }_{3}$ 

  • A
    $i > ii > iii > iv$
  • $iv > iii > i > ii$
  • C
    $iv > iii > ii > i$
  • D
    $iii > iv > ii > i$

Answer

Correct option: B.
$iv > iii > i > ii$
b
The stability of carbocation depends upon $+ M$ effect, $+ I$ effect and $+ H$ effect.

Carbocation $(i)$ shows eight hyperconjugation structures.

Carbocation $(ii)$ shows six hyperconjugation structures.

Carbocation $(iii)$ shows nine hyperconjugation structures.

Carbocation $(iv)$ shows $+M$ effect.

Therefore, the correct stability order is : $iv > iii > i > ii$

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