Question

Which of the following is the most stable cation?

• A. \(\text{CH}_{3}^{+}\)
• B. \(\text{CF}_{3}^{+}\)
• C. \((\text{CH}_{3})_{2}\text{CH}^{+}\)
• D. \(\text{CF}_{3}\text{-CH}_{2}^{+}\)

Hint:

Electron-donating groups and hyperconjugation stabilise a carbocation; strongly electron-withdrawing fluorine groups destabilise it.

Answer 1

The Correct Option is C

Step 1: Rank by substitution
Stability increases in the order methyl, primary, secondary, tertiary because more alkyl groups donate electrons.

Step 2: Apply to the options
$\text{CH}_3^{+}$ is the methyl cation, $(\text{CH}_3)_2\text{CH}^{+}$ is secondary, and the fluorinated cations are destabilised by the -I effect.

Step 3: Match the option
The secondary cation is most stable, option (C).

Final Answer:
The isopropyl carbocation is the most stable of the four. \[ \boxed{\text{(C) }(\text{CH}_{3})_{2}\text{CH}^{+}} \]