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Identify the correct statement about carbocation stability: (A) CH3(+) > CH3-CH2(+) > (CH3)2CH(+) [methyl > primary > secondary] (B) Cyclohexyl carbocation with positive charge on exocyclic carbon > methylcyclohexyl carbocation > cyclohexyl carbocation (C) tert-butyl carbocation < sec-butyl carbocation < n-butyl carbocation (D) H-C(+)H2 > D-C(+)D2 > T-C(+)T2 [hyperconjugation: H > D > T]

1. CH3(+) > CH3-CH2(+) > CH3-CH(+)-CH3
2. cyclohexyl carbocation with positive charge on exocyclic carbon > methyl-substituted cyclohexyl carbocation > cyclohexyl carbocation
3. tert-butyl carbocation < sec-butyl carbocation < n-butyl carbocation
4. H-C(+)H2 > D-C(+)D2 > T-C(+)T2

Correct answer: H-C(+)H2 > D-C(+)D2 > T-C(+)T2

Solution

(A) is wrong: correct order is methyl < primary < secondary < tertiary. (B) is wrong: exocyclic carbocations are generally less stable. (C) is wrong: tert > sec > n-butyl. (D) is correct: due to hyperconjugation, C-H stabilizes more than C-D or C-T; H-C(+)H2 > D-C(+)D2 > T-C(+)T2.

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