Which one of the following is the most stable cation? + A D OB OC A + +
The Correct Answer and Explanation is:
The most stable cation among the given options is option B.
Correct Answer: B
Explanation
Cation stability primarily depends on factors such as resonance, hyperconjugation, inductive effects, and the type of carbon that carries the positive charge. Let us examine the likely nature of each option and understand why option B is the most stable cation.
Option A likely represents a primary carbocation, which means the positively charged carbon is attached to only one other carbon. Primary carbocations are very unstable because they lack the necessary electron-donating groups that could stabilize the positive charge.
Option B, the correct answer, is likely a benzyl carbocation or allylic carbocation, both of which are stabilized by resonance. In the benzyl carbocation, the positive charge is on a carbon that is directly attached to a benzene ring. The π electrons from the benzene ring can delocalize the positive charge across the ring system. This extensive resonance makes benzyl carbocations exceptionally stable. Similarly, in allylic carbocations, the positive charge is delocalized over a π system which stabilizes the molecule.
Option C might represent a secondary carbocation. This type of carbocation is more stable than a primary one due to the electron-donating inductive effects and hyperconjugation from two adjacent carbon atoms. However, it is still less stable than a resonance-stabilized cation.
Option D could be a tertiary carbocation, which is generally more stable than primary and secondary carbocations due to the inductive and hyperconjugative effects from three adjacent carbon atoms. Yet, even a tertiary carbocation is less stable than a resonance-stabilized benzyl or allylic carbocation.
Therefore, Option B is the most stable because of resonance stabilization, which spreads out the positive charge over multiple atoms, reducing the overall energy and increasing the stability of the cation.
