Question

Which is the decreasing order of stability? (i) \(CH_3 - \overset{+}{C}H - CH_3\)
(ii) \(CH_3 - \overset{+}{C}H - O - CH_3\)
(iii) \(CH_3 \overset{+}{C}H - CO - CH_3\)

• A. \[(i)<(ii)<(iii)\]
• B. \[(ii) >> (i) >> (iii) \]
• C. \[(iii) >> (i) >> (ii)\]
• D. \[(ii) >> (iii) >> (i)\]

Hint:

+R groups stabilize carbocations strongly, while -R groups destabilize them.

Answer 1

The Correct Option is B

Concept: Carbocation stability depends on resonance and inductive effects.

Step 1: Analyze (ii).
\[ -OCH_3 \Rightarrow +R \text{ effect} \Rightarrow \text{most stable} \]

Step 2: Analyze (i).
Alkyl groups provide hyperconjugation → moderate stability.

Step 3: Analyze (iii).
\[ -COCH_3 \Rightarrow -R \text{ and } -I \Rightarrow \text{least stable} \]

Step 4: Order.
\[ (ii) \gg (i) \gg (iii) \]