See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Stability of Carbocations **Step 1: Identify the carbocation type in each option** All options show cyclohexadienyl cations (with a positive charge on the ring): - **(A)** 1,4-dimethyl-2,5-cyclohexadienyl with Ph substituent - **(B)** 2,5-cyclohexadienyl (simple) - **(C)** 1,4-cyclohexadienyl - **(D)** 1,4-dimethyl-2,5-cyclohexadienyl with Ph substituent (different position) **Step 2: Apply resonance stabilization principle** Carbocation stability increases with extended conjugation. The most stable cation has maximum resonance structures distributing the positive charge. **Step 3: Analyze option (A)** In option (A), the cyclohexadienyl cation has: - A 1,4-diene system conjugated with the positive charge - The **Ph (phenyl) group directly attached to the carbocation center** - Phenyl provides **strong electron-donating resonance** through $\pi$-electron delocalization into the empty $p$-orbital This creates additional stabilization via aromatic resonance forms. **Step 4: Compare with other options** - **(B)** and **(C)**: No electron-donating groups - **(D)**: Ph is on the ring but not directly conjugated with the positive charge center **Conclusion:** **Option (A)** is most stable because the phenyl substituent is conjugated directly with the carbocation, providing maximum resonance stabilization through aromatic electron donation to the electron-deficient carbon.