Question

Arrange the following carbocations in increasing order of their stability.
I) \((CH_3)_3C^{\oplus}\)
II) \((CH_3)_2\overset{{\oplus}}{C}H\)
III) \(\overset{{\oplus}}{C}H_3\)
IV) \(CH_3\overset{{\oplus}}{C}H_2\)

• A. I < II < IV < III
• B. I < III < IV < II
• C. II < I < III < IV
• D. III < IV < II < I

Answer 1

The Correct Option is D

To determine the stability of the given carbocations, we need to understand the concepts that affect carbocation stability:

• Hyperconjugation: More alkyl groups attached to the positively charged carbon increase stability.
• Inductive Effect: Electron-donating groups (like alkyl groups) stabilize the positive charge through the inductive effect.
• Resonance: Carbocations stabilized by resonance are highly stable. However, none of the given options involve resonance, so this will not affect the comparison.

Let's evaluate each of the given carbocations:

1. III) \(\overset{{\oplus}}{C}H_3\): This is a methyl carbocation with no alkyl groups providing hyperconjugation or inductive stabilization. It is the least stable.
2. IV) \(CH_3\overset{{\oplus}}{C}H_2\): This is a primary carbocation with one alkyl group providing some stabilization through hyperconjugation and inductive effect, but it is less stable compared to secondary and tertiary carbocations.
3. II) \((CH_3)_2\overset{{\oplus}}{C}H\): This is a secondary carbocation with two alkyl groups offering increased stability compared to primary carbocations through hyperconjugation and the inductive effect.
4. I) \((CH_3)_3C^{\oplus}\): This is a tertiary carbocation with three alkyl groups. It has the highest level of hyperconjugation and inductive effect, making it the most stable among the provided options.

Based on the above evaluations, the increasing order of stability for the given carbocations is:

III < IV < II < I

Thus, the correct answer is: III < IV < II < I.