Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
The correct order of relative stabilities for the following carbocations is: (I) (II) (III) (IV) CH ₃ C H ₂
Options
- A(I) < (II) < (III) < (IV)
- B(II) < (IV) < (III) < (I)
- C(IV) < (III) < (II) < (I)
- D(IV) < (II) < (III) < (I)
Correct answer
D. (IV) < (II) < (III) < (I)
Step-by-step solution
The stability of carbocations increases with the presence of electron-donating groups due to the dispersal of positive charge. Carbocation (I) is a p-methoxybenzyl carbocation. The - OCH ₃ group exhibits a strong +M effect, which highly stabilizes the positive charge through resonance. Carbocation (III) is a p-methylbenzyl carbocation. The - CH ₃ group stabilizes the positive charge through hyperconjugation ( +H ) and the +I effect. Since the +M effect is stronger than hyperconjugation, (I) is more stable than (III