Which of the following carbocations is the most stable: ${\text{(CH}}_3{)}_3{\text{C}}^{+}$, ${\text{CH}}_3{\text{CH}}_2^{+}$, ${\text{CH}}_2=\text{CH}-{\text{CH}}_2^{+}$, or ${\text{C}}_6{\text{H}}_5{\text{CH}}_2^{+}$?

Solution

1. Analyze the stability factors for each carbocation.
2. The ${\text{(CH}}_3{)}_3{\text{C}}^{+}$ is stabilized by hyperconjugation and inductive effects.
3. The ${\text{CH}}_2=\text{CH}-{\text{CH}}_2^{+}$ is stabilized by resonance with one double bond.
4. The ${\text{C}}_6{\text{H}}_5{\text{CH}}_2^{+}$ is stabilized by resonance with the entire aromatic ring, providing greater delocalization.
5. Hence the answer is (D).