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Consider the carbocations: (a) CH3O-C6H4-CH2(+), (b) C6H5-CH2(+), (c) CH3-C6H4-CH2(+), (d) CH3-CH2(+). What is the correct increasing order of their stability?

1. d < b < c < a
2. b < d < c < a
3. d < b < a < c
4. b < d < a < c

Correct answer: d < b < c < a

Solution

Ethyl cation (d) is a simple primary carbocation with no resonance, least stable. Unsubstituted benzyl (b) is resonance-stabilized. Adding a para-CH3 (c) donates electron density (hyperconjugation/+I), increasing stability above benzyl. A para-OCH3 (a) is a strong +M (resonance) donor, stabilizing the cation the most. Order: d < b < c < a.

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