Question

Decreasing order of stability of given carbocations is?

(1) (2) $\text{CH}_{2} = \text{CH} - \overset{\oplus}{\text{C}} \text{H}_{2}$

(3) $\text{C}_{6} \text{H}_{5} - \overset{\oplus}{\text{C}} \text{H}_{2}$ (4) $\text{CH}_{3} - \overset{\oplus}{\text{C}} \text{H} - \text{CH}_{3}$

• A. 3 > 2 > 4 > 1
• B. 1 > 3 > 4 > 2
• C. 1 > 3 >2 > 4
• D. 3 > 2 > 1 > 4

Answer 1

Answer: (C)

The factors affecting carbocation stability:
1. If carbocation is on more percentage s character carbon, it will be less stable.
2. If carbocation is attached to any electron donating group (groups those show positive inductive, mesomeric and hyperconjugation effect), its stability increases.
3. If carbocation is busy in aromatic stability, it will still be more stable than any other factor.
Preference of effects:
Aromaticity > resonance > mesomeric > hyperconjugation > inductive
(1) Aromatic
(2) $\text{CH}_{2} = \text{CH} - \overset{\oplus}{\text{C}} \text{H}_{2}$ (2 Resonating Structure)

(3)
Positive charge is more delocalised (4 Resonating Structure)
(4) $\text{CH}_{3} - \overset{\oplus}{\text{C}} \text{H} - \text{CH}_{3}$ (6 hyper conjugation)