Which one of the following carbocations is the most stable?

• A. $C_6{H}_5–C+H{2}_2$ (benzylic carbocation)
• B. $\mathrm{CH}{3}_{2}C+H$ (secondary carbocation)
• C. $\mathrm{CH}{3}_3+$ (methyl carbocation)
• D. $\mathrm{CH}{3}_{3}C+$ (tertiary carbocation)

Answer: (A)

Verified step by step guidance

1. Identify the types of carbocations given: benzylic, secondary, methyl (primary), and tertiary carbocations.
2. Recall that carbocation stability is influenced by factors such as resonance stabilization, hyperconjugation, and inductive effects.
3. Recognize that the benzylic carbocation is stabilized by resonance because the positive charge can be delocalized over the aromatic ring, which greatly increases its stability.
4. Understand that tertiary carbocations are stabilized by hyperconjugation and inductive effects from three alkyl groups, making them more stable than secondary and primary carbocations but generally less stable than resonance-stabilized carbocations like benzylic.
5. Compare the stability order: resonance-stabilized (benzylic) > tertiary > secondary > methyl (primary), concluding that the benzylic carbocation is the most stable among the options.