A) \[\text{I}>II>III\]
B) \[III>II>I\]
C) \[II>III>I\]
D) \[II>I>III\]
Correct Answer: D
Solution :
\[C{{H}_{3}}-\overset{+}{\mathop{CH}}\,-OC{{H}_{3}}\] is most stable due to resonance \[C{{H}_{3}}-\underset{(II)}{\mathop{\overset{+}{\mathop{CH}}\,-\underset{\centerdot \centerdot }{\overset{\centerdot \centerdot }{\mathop{O}}}\,-}}\,C{{H}_{3}}\overset{{}}{\longleftrightarrow}\] \[C{{H}_{3}}-CH-\underset{\centerdot \centerdot }{\overset{+}{\mathop{O}}}\,-C{{H}_{3}}\] Carbocation \[C{{H}_{3}}-\overset{+}{\mathop{C}}\,H-COC{{H}_{3}}\] is least stable due to electron withdrawing nature of carbonyl group. Carbocation \[C{{H}_{3}}-\overset{+}{\mathop{C}}\,H-C{{H}_{3}}\]is less stable than \[C{{H}_{3}}-\overset{+}{\mathop{C}}\,H-OC{{H}_{3}}\] because it stabilised only by the \[+l\] effect of the two methyl groups. \[C{{H}_{3}}\to -\overset{+}{\mathop{CH}}\,-\leftarrow C{{H}_{3}}\] Therefore, correct order of decreasing stability is \[II>I>III\]
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