Question

The most stable carbocation, among the following is :-

• A. $(CH_3)_3C- \overset{\oplus}{{C}}H-CH_3$
• B. $(CH_3)CH_2- \overset{\oplus}{{C}}H-CH_2-CH_3$
• C. $CH_3- \overset{\oplus}{{C}}H-CH_2-CH_2-CH_3$
• D. $CH_3- CH_2 -\overset{\oplus}{{C}}H_2$

Answer 1

The Correct Option is C

The stability of carbocations is determined by their ability to disperse the positive charge. More substituted carbocations are generally more stable due to hyperconjugation and inductive effects. Let's analyze each option:

1. $(CH_3)_3C- \overset{\oplus}{{C}}H-CH_3$: This is a tertiary carbocation, which is typically very stable due to hyperconjugation from nine hydrogen atoms.
2. $(CH_3)CH_2- \overset{\oplus}{{C}}H-CH_2-CH_3$: This is a secondary carbocation, which is less stable than a tertiary carbocation but more stable than primary ones.
3. $CH_3- \overset{\oplus}{{C}}H-CH_2-CH_2-CH_3$: This is a secondary carbocation with possible additional stabilization. It is a cyclic structure (cyclohexyl), providing additional stability, making it more stable than the other secondary carbocation.
4. $CH_3- CH_2 -\overset{\oplus}{{C}}H_2$: This is a primary carbocation, which is generally the least stable due to minimal hyperconjugation.

Among the given options, the most stable carbocation is $CH_3- \overset{\oplus}{{C}}H-CH_2-CH_2-CH_3$. This is primarily because it is a possible resonance-stabilized and cyclic structure, often enhancing stability.

In summary, the choice can be justified as follows:

• The tertiary carbocation $(CH_3)_3C- \overset{\oplus}{{C}}H-CH_3$ is generally stable but does not exhibit any additional stabilization beyond simple hyperconjugation.
• The secondary carbocation $CH_3- \overset{\oplus}{{C}}H-CH_2-CH_2-CH_3$ may benefit from extra stabilization due to resonance in a cyclic structure, making it the most stable.