How many of the following species show σ-hyperconjugation (delocalisation of a C-H σ bond into an empty p orbital of a carbocation) ?

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Only carbocations are counted, as the question is about donation into an empty p orbital.

CH₃-CH₂⁺ : α-H present, counts.

(CH₃)₃C⁺ : α-H present, counts.

The benzyl-type cation has its positive carbon bonded only to the ring and H, and the tert-butyl group has no α-H, so it does not count. Toluene, m-xylene and isobutene show σ-π hyperconjugation, not σ-p.

Answer = 2.

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