Question

What is the stability order of carbocations?

• A. Primary \(>\) Secondary \(>\) Tertiary
• B. Secondary \(>\) Primary \(>\) Tertiary
• C. Tertiary \(>\) Secondary \(>\) Primary
• D. Primary \(>\) Tertiary \(>\) Secondary

Hint:

More alkyl groups attached to a carbocation increase its stability due to hyperconjugation and the +I inductive effect.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question requires the ranking of alkyl carbocations (\( R_3C^+ \), \( R_2CH^+ \), \( RCH_2^+ \)) based on their relative stability.
Step 2: Key Formula or Approach:
Carbocation stability is governed by:
1. Inductive Effect (\( +I \)): Alkyl groups donate electron density to the electron-deficient positive carbon.
2. Hyperconjugation: The overlap of \( \sigma \)-bonds (C-H) with the empty p-orbital of the carbocation.
Step 3: Detailed Explanation:
- Tertiary (\( 3^\circ \)) carbocation: Has three alkyl groups. It has the maximum \( +I \) effect and the most hyperconjugative structures.
- Secondary (\( 2^\circ \)) carbocation: Has two alkyl groups, providing moderate stabilization.
- Primary (\( 1^\circ \)) carbocation: Has only one alkyl group, providing the least stabilization.
The more the positive charge is dispersed among the surrounding groups, the more stable the carbocation becomes.
Step 4: Final Answer:
The stability order is: Tertiary \(>\) Secondary \(>\) Primary.