Which of the following carbocations is the most stable?

• A. $\mathrm{CH}{3}_1–\mathrm{CH}{2}_1+$ (ethyl carbocation)
• B. $\mathrm{CH}{3}_3–C+$ (tert-butyl carbocation)
• C. $C_6{H}_5–C+$ (benzylic carbocation)
• D. $\mathrm{CH}{3}_2–\mathrm{CH}+$ (isopropyl carbocation)

Answer: (C)

Verified step by step guidance

1. Identify the structure of each carbocation: ethyl carbocation (CH\3-CH\2\+), tert-butyl carbocation ((CH\3)\3C\+), benzylic carbocation (C\6H\5-CH\+), and isopropyl carbocation (CH\3-CH\+).
2. Recall that carbocation stability is influenced by factors such as alkyl substitution (hyperconjugation), resonance stabilization, and inductive effects.
3. Evaluate the ethyl carbocation: it is a primary carbocation with minimal hyperconjugation and no resonance, so it is relatively unstable.
4. Evaluate the tert-butyl carbocation: it is a tertiary carbocation with three alkyl groups providing strong hyperconjugation and inductive stabilization, making it quite stable.
5. Evaluate the benzylic carbocation: it is stabilized by resonance with the aromatic ring, allowing the positive charge to be delocalized over the benzene ring, which generally provides greater stability than hyperconjugation alone.