Question
The compound which gives the most stable carbonium ion on dehydration is :
A.
\[C{{H}_{3}}\underset{\begin{smallmatrix}
|\,\,\,\,\, \\
C{{H}_{3}}
\end{smallmatrix}}{\mathop{-CH-}}\,C{{H}_{2}}OH\]
B.
\[C{{H}_{3}}\underset{\begin{smallmatrix}
| \\
\,\,\,\,C{{H}_{3}}
\end{smallmatrix}}{\overset{\begin{smallmatrix}
\,\,\,\,C{{H}_{3}} \\
|
\end{smallmatrix}}{\mathop{-C-}}}\,OH\]
C.
\[C{{H}_{3}}C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}OH\]
D.
\[C{{H}_{3}}\underset{\begin{smallmatrix}
|\,\,\,\,\, \\
OH\,\,
\end{smallmatrix}}{\mathop{-CH-}}\,C{{H}_{2}}-C{{H}_{3}}\]
Answer :
\[C{{H}_{3}}\underset{\begin{smallmatrix}
| \\
\,\,\,\,C{{H}_{3}}
\end{smallmatrix}}{\overset{\begin{smallmatrix}
\,\,\,\,C{{H}_{3}} \\
|
\end{smallmatrix}}{\mathop{-C-}}}\,OH\]
Solution :
NOTE : The order of stability of carbonium ion is tertiary > secondary > primary > methyl
Tertiary carbonium ions ( formed in B ) are more stable because of electron repelling ( $$ + I$$ effect ) nature of $$C{H_3}$$ group due to which the $$+ve$$ harge gets dispersed and also due to hyperconjugation.